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 $217.79   6.872%   $232.7565   $232.76   $232.75   $232.80  
  Purchase #2 $94.55   11.251%   $105.1878   $105.19   $105.20   $105.20  
  Purchase #3 $176.61   7.109%   $189.1652   $189.17   $189.15   $189.20  
  Purchase #4 $211.56   3.536%   $219.0408   $219.04   $219.05   $219.00  
  Purchase #5 $123.47   10.287%   $136.1714   $136.17   $136.15   $136.20  
  Purchase #6 $50.52   8.610%   $54.8698   $54.87   $54.85   $54.90  
  Purchase #7 $102.62   4.135%   $106.8633   $106.86   $106.85   $106.90  
  7 purchase totals = $977.12       $1,044.0548   $1,044.06   $1,044.00   $1,044.20