Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $185.63   9.164%   $202.6411   $202.64   $202.65   $202.60  
  Purchase #2 $106.90   10.711%   $118.3501   $118.35   $118.35   $118.40  
  Purchase #3 $179.54   7.445%   $192.9068   $192.91   $192.90   $192.90  
  Purchase #4 $204.57   6.797%   $218.4746   $218.47   $218.45   $218.50  
  Purchase #5 $194.60   12.619%   $219.1566   $219.16   $219.15   $219.20  
  Purchase #6 $181.32   7.552%   $195.0133   $195.01   $195.00   $195.00  
  Purchase #7 $210.52   7.674%   $226.6753   $226.68   $226.70   $226.70  
  7 purchase totals = $1,263.08       $1,373.2178   $1,373.22   $1,373.20   $1,373.30