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 $82.39   13.463%   $93.4822   $93.48   $93.50   $93.50  
  Purchase #2 $246.45   13.235%   $279.0677   $279.07   $279.05   $279.10  
  Purchase #3 $138.52   12.741%   $156.1688   $156.17   $156.15   $156.20  
  Purchase #4 $166.46   8.802%   $181.1118   $181.11   $181.10   $181.10  
  Purchase #5 $124.58   3.197%   $128.5628   $128.56   $128.55   $128.60  
  Purchase #6 $184.73   5.139%   $194.2233   $194.22   $194.20   $194.20  
  Purchase #7 $149.50   13.526%   $169.7214   $169.72   $169.70   $169.70  
  7 purchase totals = $1,092.63       $1,202.3380   $1,202.33   $1,202.25   $1,202.40