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 $119.34   10.826%   $132.2597   $132.26   $132.25   $132.30  
  Purchase #2 $155.65   7.408%   $167.1806   $167.18   $167.20   $167.20  
  Purchase #3 $105.29   10.211%   $116.0412   $116.04   $116.05   $116.00  
  Purchase #4 $214.82   12.447%   $241.5586   $241.56   $241.55   $241.60  
  Purchase #5 $83.28   9.395%   $91.1042   $91.10   $91.10   $91.10  
  Purchase #6 $236.26   6.540%   $251.7114   $251.71   $251.70   $251.70  
  Purchase #7 $168.91   7.221%   $181.107   $181.11   $181.10   $181.10  
  7 purchase totals = $1,083.55       $1,180.9627   $1,180.96   $1,180.95   $1,181.00