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 $232.76   5.527%   $245.6246   $245.62   $245.60   $245.60  
  Purchase #2 $147.45   7.162%   $158.0104   $158.01   $158.00   $158.00  
  Purchase #3 $118.53   12.388%   $133.2135   $133.21   $133.20   $133.20  
  Purchase #4 $10.33   9.504%   $11.3118   $11.31   $11.30   $11.30  
  Purchase #5 $95.57   10.191%   $105.3095   $105.31   $105.30   $105.30  
  Purchase #6 $206.40   11.657%   $230.46   $230.46   $230.45   $230.50  
  Purchase #7 $94.52   7.693%   $101.7914   $101.79   $101.80   $101.80  
  7 purchase totals = $905.56       $985.7212   $985.71   $985.65   $985.70