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 $94.93   6.779%   $101.3653   $101.37   $101.35   $101.40  
  Purchase #2 $84.37   11.782%   $94.3105   $94.31   $94.30   $94.30  
  Purchase #3 $70.52   5.574%   $74.4508   $74.45   $74.45   $74.50  
  Purchase #4 $197.90   9.229%   $216.1642   $216.16   $216.15   $216.20  
  Purchase #5 $151.73   8.526%   $164.6665   $164.67   $164.65   $164.70  
  Purchase #6 $188.37   12.807%   $212.4945   $212.49   $212.50   $212.50  
  Purchase #7 $119.79   12.721%   $135.0285   $135.03   $135.05   $135.00  
  7 purchase totals = $907.61       $998.4803   $998.48   $998.45   $998.60