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 $45.73   3.368%   $47.2702   $47.27   $47.25   $47.30  
  Purchase #2 $60.51   7.492%   $65.0434   $65.04   $65.05   $65.00  
  Purchase #3 $24.87   7.231%   $26.6683   $26.67   $26.65   $26.70  
  Purchase #4 $165.51   6.493%   $176.2566   $176.26   $176.25   $176.30  
  Purchase #5 $130.38   3.781%   $135.3097   $135.31   $135.30   $135.30  
  Purchase #6 $236.97   3.855%   $246.1052   $246.11   $246.10   $246.10  
  Purchase #7 $99.52   3.833%   $103.3346   $103.33   $103.35   $103.30  
  7 purchase totals = $763.49       $799.9880   $799.99   $799.95   $800.00