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 $162.33   13.468%   $184.1926   $184.19   $184.20   $184.20  
  Purchase #2 $110.52   6.723%   $117.9503   $117.95   $117.95   $118.00  
  Purchase #3 $225.59   10.633%   $249.577   $249.58   $249.60   $249.60  
  Purchase #4 $43.83   11.621%   $48.9235   $48.92   $48.90   $48.90  
  Purchase #5 $91.54   5.502%   $96.5765   $96.58   $96.60   $96.60  
  Purchase #6 $231.34   11.701%   $258.4091   $258.41   $258.40   $258.40  
  Purchase #7 $79.96   10.502%   $88.3574   $88.36   $88.35   $88.40  
  7 purchase totals = $945.11       $1,043.9864   $1,043.99   $1,044.00   $1,044.10