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 $132.85   12.604%   $149.5944   $149.59   $149.60   $149.60  
  Purchase #2 $177.78   10.434%   $196.3296   $196.33   $196.35   $196.30  
  Purchase #3 $100.31   5.851%   $106.1791   $106.18   $106.20   $106.20  
  Purchase #4 $130.72   7.671%   $140.7475   $140.75   $140.75   $140.70  
  Purchase #5 $178.93   8.616%   $194.3466   $194.35   $194.35   $194.30  
  Purchase #6 $152.93   5.748%   $161.7204   $161.72   $161.70   $161.70  
  Purchase #7 $234.65   8.450%   $254.4779   $254.48   $254.50   $254.50  
  7 purchase totals = $1,108.17       $1,203.3955   $1,203.40   $1,203.45   $1,203.30