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 $177.58   8.243%   $192.2179   $192.22   $192.20   $192.20  
  Purchase #2 $230.72   3.849%   $239.6004   $239.60   $239.60   $239.60  
  Purchase #3 $71.98   8.107%   $77.8154   $77.82   $77.80   $77.80  
  Purchase #4 $155.99   11.462%   $173.8696   $173.87   $173.85   $173.90  
  Purchase #5 $241.40   9.165%   $263.5243   $263.52   $263.50   $263.50  
  Purchase #6 $48.29   9.817%   $53.0306   $53.03   $53.05   $53.00  
  Purchase #7 $83.81   12.441%   $94.2368   $94.24   $94.25   $94.20  
  7 purchase totals = $1,009.77       $1,094.2950   $1,094.30   $1,094.25   $1,094.20