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 $243.79   13.146%   $275.8386   $275.84   $275.85   $275.80  
  Purchase #2 $118.92   6.127%   $126.2062   $126.21   $126.20   $126.20  
  Purchase #3 $83.52   13.428%   $94.7351   $94.74   $94.75   $94.70  
  Purchase #4 $152.80   9.752%   $167.7011   $167.70   $167.70   $167.70  
  Purchase #5 $54.77   12.103%   $61.3988   $61.40   $61.40   $61.40  
  Purchase #6 $153.32   3.657%   $158.9269   $158.93   $158.95   $158.90  
  Purchase #7 $197.47   10.454%   $218.1135   $218.11   $218.10   $218.10  
  7 purchase totals = $1,004.59       $1,102.9202   $1,102.93   $1,102.95   $1,102.80