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 $192.44   13.291%   $218.0172   $218.02   $218.00   $218.00  
  Purchase #2 $189.68   13.539%   $215.3608   $215.36   $215.35   $215.40  
  Purchase #3 $33.26   7.272%   $35.6787   $35.68   $35.70   $35.70  
  Purchase #4 $156.30   8.507%   $169.5964   $169.60   $169.60   $169.60  
  Purchase #5 $24.91   3.721%   $25.8369   $25.84   $25.85   $25.80  
  Purchase #6 $213.37   10.138%   $235.0015   $235.00   $235.00   $235.00  
  Purchase #7 $105.85   7.236%   $113.5093   $113.51   $113.50   $113.50  
  7 purchase totals = $915.81       $1,013.0008   $1,013.01   $1,013.00   $1,013.00