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 $82.81   12.396%   $93.0751   $93.08   $93.10   $93.10  
  Purchase #2 $95.28   6.676%   $101.6409   $101.64   $101.65   $101.60  
  Purchase #3 $174.64   4.771%   $182.9721   $182.97   $182.95   $183.00  
  Purchase #4 $222.97   8.107%   $241.0462   $241.05   $241.05   $241.00  
  Purchase #5 $179.82   11.631%   $200.7349   $200.73   $200.75   $200.70  
  Purchase #6 $188.52   11.593%   $210.3751   $210.38   $210.40   $210.40  
  Purchase #7 $58.62   8.434%   $63.564   $63.56   $63.55   $63.60  
  7 purchase totals = $1,002.66       $1,093.4083   $1,093.41   $1,093.45   $1,093.40