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 $166.52   12.385%   $187.1435   $187.14   $187.15   $187.10  
  Purchase #2 $165.73   8.723%   $180.1866   $180.19   $180.20   $180.20  
  Purchase #3 $243.62   13.617%   $276.7937   $276.79   $276.80   $276.80  
  Purchase #4 $45.56   5.169%   $47.915   $47.92   $47.90   $47.90  
  Purchase #5 $75.35   10.485%   $83.2504   $83.25   $83.25   $83.30  
  Purchase #6 $62.83   4.412%   $65.6021   $65.60   $65.60   $65.60  
  Purchase #7 $212.36   10.195%   $234.0101   $234.01   $234.00   $234.00  
  7 purchase totals = $971.97       $1,074.9014   $1,074.90   $1,074.90   $1,074.90