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 $231.97   9.505%   $254.0187   $254.02   $254.00   $254.00  
  Purchase #2 $57.81   9.757%   $63.4505   $63.45   $63.45   $63.50  
  Purchase #3 $225.40   7.188%   $241.6018   $241.60   $241.60   $241.60  
  Purchase #4 $67.54   10.341%   $74.5243   $74.52   $74.50   $74.50  
  Purchase #5 $203.92   4.220%   $212.5254   $212.53   $212.55   $212.50  
  Purchase #6 $101.79   6.601%   $108.5092   $108.51   $108.50   $108.50  
  Purchase #7 $13.62   5.870%   $14.4195   $14.42   $14.40   $14.40  
  7 purchase totals = $902.05       $969.0494   $969.05   $969.00   $969.00