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 $244.42   7.414%   $262.5413   $262.54   $262.55   $262.50  
  Purchase #2 $211.78   6.222%   $224.957   $224.96   $224.95   $225.00  
  Purchase #3 $88.46   5.866%   $93.6491   $93.65   $93.65   $93.60  
  Purchase #4 $18.70   4.611%   $19.5623   $19.56   $19.55   $19.60  
  Purchase #5 $92.62   4.838%   $97.101   $97.10   $97.10   $97.10  
  Purchase #6 $102.79   5.753%   $108.7035   $108.70   $108.70   $108.70  
  Purchase #7 $67.55   8.835%   $73.518   $73.52   $73.50   $73.50  
  7 purchase totals = $826.32       $880.0322   $880.03   $880.00   $880.00