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 $154.31   8.263%   $167.0606   $167.06   $167.05   $167.10  
  Purchase #2 $157.63   11.332%   $175.4926   $175.49   $175.50   $175.50  
  Purchase #3 $104.48   11.546%   $116.5433   $116.54   $116.55   $116.50  
  Purchase #4 $170.56   7.857%   $183.9609   $183.96   $183.95   $184.00  
  Purchase #5 $186.69   13.748%   $212.3561   $212.36   $212.35   $212.40  
  Purchase #6 $43.90   10.711%   $48.6021   $48.60   $48.60   $48.60  
  Purchase #7 $132.57   13.591%   $150.5876   $150.59   $150.60   $150.60  
  7 purchase totals = $950.14       $1,054.6032   $1,054.60   $1,054.60   $1,054.70