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 $171.26   4.508%   $178.9804   $178.98   $179.00   $179.00  
  Purchase #2 $27.80   13.582%   $31.5758   $31.58   $31.60   $31.60  
  Purchase #3 $160.46   5.668%   $169.5549   $169.55   $169.55   $169.60  
  Purchase #4 $142.47   11.401%   $158.713   $158.71   $158.70   $158.70  
  Purchase #5 $150.28   12.233%   $168.6638   $168.66   $168.65   $168.70  
  Purchase #6 $54.98   6.758%   $58.6955   $58.70   $58.70   $58.70  
  Purchase #7 $20.74   13.220%   $23.4818   $23.48   $23.50   $23.50  
  7 purchase totals = $727.99       $789.6652   $789.66   $789.70   $789.80