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 $193.94   5.570%   $204.7425   $204.74   $204.75   $204.70  
  Purchase #2 $234.43   9.705%   $257.1814   $257.18   $257.20   $257.20  
  Purchase #3 $239.30   3.132%   $246.7949   $246.79   $246.80   $246.80  
  Purchase #4 $143.86   11.220%   $160.0011   $160.00   $160.00   $160.00  
  Purchase #5 $133.87   7.132%   $143.4176   $143.42   $143.40   $143.40  
  Purchase #6 $184.66   5.200%   $194.2623   $194.26   $194.25   $194.30  
  Purchase #7 $45.28   9.303%   $49.4924   $49.49   $49.50   $49.50  
  7 purchase totals = $1,175.34       $1,255.8922   $1,255.88   $1,255.90   $1,255.90