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 $167.48   12.228%   $187.9595   $187.96   $187.95   $188.00  
  Purchase #2 $196.85   3.507%   $203.7535   $203.75   $203.75   $203.80  
  Purchase #3 $219.84   7.119%   $235.4904   $235.49   $235.50   $235.50  
  Purchase #4 $94.99   11.305%   $105.7286   $105.73   $105.75   $105.70  
  Purchase #5 $122.51   5.467%   $129.2076   $129.21   $129.20   $129.20  
  Purchase #6 $193.61   8.114%   $209.3195   $209.32   $209.30   $209.30  
  Purchase #7 $81.25   4.354%   $84.7876   $84.79   $84.80   $84.80  
  7 purchase totals = $1,076.53       $1,156.2467   $1,156.25   $1,156.25   $1,156.30