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 $88.70   6.858%   $94.783   $94.78   $94.80   $94.80  
  Purchase #2 $129.72   10.443%   $143.2667   $143.27   $143.25   $143.30  
  Purchase #3 $101.91   8.157%   $110.2228   $110.22   $110.20   $110.20  
  Purchase #4 $237.65   13.232%   $269.0958   $269.10   $269.10   $269.10  
  Purchase #5 $37.62   10.194%   $41.455   $41.46   $41.45   $41.50  
  Purchase #6 $91.73   5.274%   $96.5678   $96.57   $96.55   $96.60  
  Purchase #7 $113.90   6.691%   $121.521   $121.52   $121.50   $121.50  
  7 purchase totals = $801.23       $876.9121   $876.92   $876.85   $877.00