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 $226.25   8.811%   $246.1849   $246.18   $246.20   $246.20  
  Purchase #2 $180.83   5.586%   $190.9312   $190.93   $190.95   $190.90  
  Purchase #3 $35.70   6.288%   $37.9448   $37.94   $37.95   $37.90  
  Purchase #4 $58.92   12.147%   $66.077   $66.08   $66.10   $66.10  
  Purchase #5 $11.97   8.307%   $12.9643   $12.96   $12.95   $13.00  
  Purchase #6 $31.91   4.145%   $33.2327   $33.23   $33.25   $33.20  
  Purchase #7 $111.85   5.370%   $117.8563   $117.86   $117.85   $117.90  
  7 purchase totals = $657.43       $705.1912   $705.18   $705.25   $705.20