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 $197.45   3.117%   $203.6045   $203.60   $203.60   $203.60  
  Purchase #2 $126.37   8.839%   $137.5398   $137.54   $137.55   $137.50  
  Purchase #3 $88.40   12.479%   $99.4314   $99.43   $99.45   $99.40  
  Purchase #4 $172.78   6.712%   $184.377   $184.38   $184.40   $184.40  
  Purchase #5 $88.74   5.770%   $93.8603   $93.86   $93.85   $93.90  
  Purchase #6 $116.52   8.409%   $126.3182   $126.32   $126.30   $126.30  
  Purchase #7 $6.53   10.585%   $7.2212   $7.22   $7.20   $7.20  
  7 purchase totals = $796.79       $852.3524   $852.35   $852.35   $852.30