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 $245.37   6.365%   $260.9878   $260.99   $261.00   $261.00  
  Purchase #2 $155.31   13.729%   $176.6325   $176.63   $176.65   $176.60  
  Purchase #3 $176.30   6.290%   $187.3893   $187.39   $187.40   $187.40  
  Purchase #4 $167.75   13.121%   $189.7605   $189.76   $189.75   $189.80  
  Purchase #5 $67.95   11.191%   $75.5543   $75.55   $75.55   $75.60  
  Purchase #6 $218.45   12.851%   $246.523   $246.52   $246.50   $246.50  
  Purchase #7 $134.31   7.481%   $144.3577   $144.36   $144.35   $144.40  
  7 purchase totals = $1,165.44       $1,281.2051   $1,281.20   $1,281.20   $1,281.30