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 $114.51   8.151%   $123.8437   $123.84   $123.85   $123.80  
  Purchase #2 $62.73   9.546%   $68.7182   $68.72   $68.70   $68.70  
  Purchase #3 $181.77   7.134%   $194.7375   $194.74   $194.75   $194.70  
  Purchase #4 $43.59   6.252%   $46.3152   $46.32   $46.30   $46.30  
  Purchase #5 $28.35   8.590%   $30.7853   $30.79   $30.80   $30.80  
  Purchase #6 $44.71   9.631%   $49.016   $49.02   $49.00   $49.00  
  Purchase #7 $243.96   4.328%   $254.5186   $254.52   $254.50   $254.50  
  7 purchase totals = $719.62       $767.9345   $767.95   $767.90   $767.80