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 $188.91   8.532%   $205.0278   $205.03   $205.05   $205.00  
  Purchase #2 $25.30   10.432%   $27.9393   $27.94   $27.95   $27.90  
  Purchase #3 $131.35   10.140%   $144.6689   $144.67   $144.65   $144.70  
  Purchase #4 $23.98   11.767%   $26.8017   $26.80   $26.80   $26.80  
  Purchase #5 $70.47   3.481%   $72.9231   $72.92   $72.90   $72.90  
  Purchase #6 $165.26   4.809%   $173.2074   $173.21   $173.20   $173.20  
  Purchase #7 $68.30   6.502%   $72.7409   $72.74   $72.75   $72.70  
  7 purchase totals = $673.57       $723.3091   $723.31   $723.30   $723.20