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 $78.41   7.653%   $84.4107   $84.41   $84.40   $84.40  
  Purchase #2 $202.28   9.601%   $221.7009   $221.70   $221.70   $221.70  
  Purchase #3 $86.84   11.824%   $97.108   $97.11   $97.10   $97.10  
  Purchase #4 $126.66   13.315%   $143.5248   $143.52   $143.50   $143.50  
  Purchase #5 $238.35   8.331%   $258.2069   $258.21   $258.20   $258.20  
  Purchase #6 $155.55   13.704%   $176.8666   $176.87   $176.85   $176.90  
  Purchase #7 $237.45   11.486%   $264.7235   $264.72   $264.70   $264.70  
  7 purchase totals = $1,125.54       $1,246.5414   $1,246.54   $1,246.45   $1,246.50