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 $182.30   10.657%   $201.7277   $201.73   $201.75   $201.70  
  Purchase #2 $150.84   7.834%   $162.6568   $162.66   $162.65   $162.70  
  Purchase #3 $223.52   4.141%   $232.776   $232.78   $232.80   $232.80  
  Purchase #4 $142.38   6.474%   $151.5977   $151.60   $151.60   $151.60  
  Purchase #5 $61.34   5.790%   $64.8916   $64.89   $64.90   $64.90  
  Purchase #6 $169.37   12.782%   $191.0189   $191.02   $191.00   $191.00  
  Purchase #7 $222.29   12.258%   $249.5383   $249.54   $249.55   $249.50  
  7 purchase totals = $1,152.04       $1,254.2070   $1,254.22   $1,254.25   $1,254.20