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 $232.61   9.279%   $254.1939   $254.19   $254.20   $254.20  
  Purchase #2 $11.96   4.826%   $12.5372   $12.54   $12.55   $12.50  
  Purchase #3 $249.41   4.384%   $260.3441   $260.34   $260.35   $260.30  
  Purchase #4 $165.85   13.220%   $187.7754   $187.78   $187.80   $187.80  
  Purchase #5 $209.98   4.657%   $219.7588   $219.76   $219.75   $219.80  
  Purchase #6 $104.50   11.765%   $116.7944   $116.79   $116.80   $116.80  
  Purchase #7 $146.77   3.324%   $151.6486   $151.65   $151.65   $151.60  
  7 purchase totals = $1,121.08       $1,203.0524   $1,203.05   $1,203.10   $1,203.00