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 $89.25   10.318%   $98.4588   $98.46   $98.45   $98.50  
  Purchase #2 $180.84   7.584%   $194.5549   $194.55   $194.55   $194.60  
  Purchase #3 $182.26   11.573%   $203.3529   $203.35   $203.35   $203.40  
  Purchase #4 $202.86   6.481%   $216.0074   $216.01   $216.00   $216.00  
  Purchase #5 $123.55   7.369%   $132.6544   $132.65   $132.65   $132.70  
  Purchase #6 $242.38   12.361%   $272.3406   $272.34   $272.35   $272.30  
  Purchase #7 $49.59   9.812%   $54.4558   $54.46   $54.45   $54.50  
  7 purchase totals = $1,070.73       $1,171.8248   $1,171.82   $1,171.80   $1,172.00