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 $158.25   6.812%   $169.03   $169.03   $169.05   $169.00  
  Purchase #2 $187.55   13.546%   $212.9555   $212.96   $212.95   $213.00  
  Purchase #3 $147.61   6.452%   $157.1338   $157.13   $157.15   $157.10  
  Purchase #4 $170.31   5.220%   $179.2002   $179.20   $179.20   $179.20  
  Purchase #5 $58.69   9.148%   $64.059   $64.06   $64.05   $64.10  
  Purchase #6 $178.78   12.256%   $200.6913   $200.69   $200.70   $200.70  
  Purchase #7 $245.67   5.850%   $260.0417   $260.04   $260.05   $260.00  
  7 purchase totals = $1,146.86       $1,243.1115   $1,243.11   $1,243.15   $1,243.10