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 $116.79   9.386%   $127.7519   $127.75   $127.75   $127.80  
  Purchase #2 $46.28   4.183%   $48.2159   $48.22   $48.20   $48.20  
  Purchase #3 $80.90   12.796%   $91.252   $91.25   $91.25   $91.30  
  Purchase #4 $222.26   7.426%   $238.765   $238.77   $238.75   $238.80  
  Purchase #5 $101.73   5.516%   $107.3414   $107.34   $107.35   $107.30  
  Purchase #6 $183.89   3.475%   $190.2802   $190.28   $190.30   $190.30  
  Purchase #7 $190.94   5.812%   $202.0374   $202.04   $202.05   $202.00  
  7 purchase totals = $942.79       $1,005.6438   $1,005.65   $1,005.65   $1,005.70