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 $236.25   10.167%   $260.2695   $260.27   $260.25   $260.30  
  Purchase #2 $144.96   4.387%   $151.3194   $151.32   $151.30   $151.30  
  Purchase #3 $80.54   4.519%   $84.1796   $84.18   $84.20   $84.20  
  Purchase #4 $242.65   3.521%   $251.1937   $251.19   $251.20   $251.20  
  Purchase #5 $24.67   4.753%   $25.8426   $25.84   $25.85   $25.80  
  Purchase #6 $212.58   7.774%   $229.106   $229.11   $229.10   $229.10  
  Purchase #7 $120.74   11.211%   $134.2762   $134.28   $134.30   $134.30  
  7 purchase totals = $1,062.39       $1,136.1870   $1,136.19   $1,136.20   $1,136.20