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 $29.81   9.852%   $32.7469   $32.75   $32.75   $32.70  
  Purchase #2 $115.65   11.402%   $128.8364   $128.84   $128.85   $128.80  
  Purchase #3 $162.26   4.830%   $170.0972   $170.10   $170.10   $170.10  
  Purchase #4 $202.38   4.256%   $210.9933   $210.99   $211.00   $211.00  
  Purchase #5 $118.80   13.154%   $134.427   $134.43   $134.45   $134.40  
  Purchase #6 $146.61   10.691%   $162.2841   $162.28   $162.30   $162.30  
  Purchase #7 $197.26   12.513%   $221.9431   $221.94   $221.95   $221.90  
  7 purchase totals = $972.77       $1,061.3280   $1,061.33   $1,061.40   $1,061.20