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 $29.76   8.733%   $32.3589   $32.36   $32.35   $32.40  
  Purchase #2 $154.57   9.479%   $169.2217   $169.22   $169.20   $169.20  
  Purchase #3 $245.99   8.535%   $266.9852   $266.99   $267.00   $267.00  
  Purchase #4 $129.30   13.198%   $146.365   $146.37   $146.35   $146.40  
  Purchase #5 $162.74   3.343%   $168.1804   $168.18   $168.20   $168.20  
  Purchase #6 $179.85   7.574%   $193.4718   $193.47   $193.45   $193.50  
  Purchase #7 $23.44   9.424%   $25.649   $25.65   $25.65   $25.60  
  7 purchase totals = $925.65       $1,002.2320   $1,002.24   $1,002.20   $1,002.30