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 $136.42   13.106%   $154.2992   $154.30   $154.30   $154.30  
  Purchase #2 $200.67   9.117%   $218.9651   $218.97   $218.95   $219.00  
  Purchase #3 $75.98   8.200%   $82.2104   $82.21   $82.20   $82.20  
  Purchase #4 $233.65   12.641%   $263.1857   $263.19   $263.20   $263.20  
  Purchase #5 $166.50   13.755%   $189.4021   $189.40   $189.40   $189.40  
  Purchase #6 $155.96   13.122%   $176.4251   $176.43   $176.45   $176.40  
  Purchase #7 $118.40   13.869%   $134.8209   $134.82   $134.80   $134.80  
  7 purchase totals = $1,087.58       $1,219.3085   $1,219.32   $1,219.30   $1,219.30