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 $190.78   5.627%   $201.5152   $201.52   $201.50   $201.50  
  Purchase #2 $94.48   3.102%   $97.4108   $97.41   $97.40   $97.40  
  Purchase #3 $246.45   4.319%   $257.0942   $257.09   $257.10   $257.10  
  Purchase #4 $68.57   3.267%   $70.8102   $70.81   $70.80   $70.80  
  Purchase #5 $75.63   10.675%   $83.7035   $83.70   $83.70   $83.70  
  Purchase #6 $203.48   3.303%   $210.2009   $210.20   $210.20   $210.20  
  Purchase #7 $92.46   8.315%   $100.148   $100.15   $100.15   $100.10  
  7 purchase totals = $971.85       $1,020.8828   $1,020.88   $1,020.85   $1,020.80