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 $48.53   8.361%   $52.5876   $52.59   $52.60   $52.60  
  Purchase #2 $133.35   9.551%   $146.0863   $146.09   $146.10   $146.10  
  Purchase #3 $107.64   5.140%   $113.1727   $113.17   $113.15   $113.20  
  Purchase #4 $138.33   12.782%   $156.0113   $156.01   $156.00   $156.00  
  Purchase #5 $150.73   9.866%   $165.601   $165.60   $165.60   $165.60  
  Purchase #6 $119.94   11.228%   $133.4069   $133.41   $133.40   $133.40  
  Purchase #7 $84.76   8.310%   $91.8036   $91.80   $91.80   $91.80  
  7 purchase totals = $783.28       $858.6694   $858.67   $858.65   $858.70