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 $208.72   10.764%   $231.1866   $231.19   $231.20   $231.20  
  Purchase #2 $92.78   3.575%   $96.0969   $96.10   $96.10   $96.10  
  Purchase #3 $107.66   11.343%   $119.8719   $119.87   $119.85   $119.90  
  Purchase #4 $13.59   9.647%   $14.901   $14.90   $14.90   $14.90  
  Purchase #5 $58.66   6.720%   $62.602   $62.60   $62.60   $62.60  
  Purchase #6 $169.65   6.266%   $180.2803   $180.28   $180.30   $180.30  
  Purchase #7 $27.91   5.432%   $29.4261   $29.43   $29.45   $29.40  
  7 purchase totals = $678.97       $734.3648   $734.37   $734.40   $734.40