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 $197.73   3.254%   $204.1641   $204.16   $204.15   $204.20  
  Purchase #2 $85.82   11.816%   $95.9605   $95.96   $95.95   $96.00  
  Purchase #3 $166.30   8.185%   $179.9117   $179.91   $179.90   $179.90  
  Purchase #4 $46.36   13.306%   $52.5287   $52.53   $52.55   $52.50  
  Purchase #5 $78.84   12.750%   $88.8921   $88.89   $88.90   $88.90  
  Purchase #6 $161.45   5.132%   $169.7356   $169.74   $169.75   $169.70  
  Purchase #7 $244.44   5.550%   $258.0064   $258.01   $258.00   $258.00  
  7 purchase totals = $980.94       $1,049.1991   $1,049.20   $1,049.20   $1,049.20