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 $232.65   11.768%   $260.0283   $260.03   $260.05   $260.00  
  Purchase #2 $119.49   3.156%   $123.2611   $123.26   $123.25   $123.30  
  Purchase #3 $193.41   13.221%   $218.9807   $218.98   $219.00   $219.00  
  Purchase #4 $160.86   4.337%   $167.8365   $167.84   $167.85   $167.80  
  Purchase #5 $8.51   9.198%   $9.2927   $9.29   $9.30   $9.30  
  Purchase #6 $220.96   8.139%   $238.9439   $238.94   $238.95   $238.90  
  Purchase #7 $150.86   9.177%   $164.7044   $164.70   $164.70   $164.70  
  7 purchase totals = $1,086.74       $1,183.0476   $1,183.04   $1,183.10   $1,183.00