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 $247.39   11.464%   $275.7508   $275.75   $275.75   $275.80  
  Purchase #2 $241.34   12.637%   $271.8381   $271.84   $271.85   $271.80  
  Purchase #3 $177.49   12.534%   $199.7366   $199.74   $199.75   $199.70  
  Purchase #4 $160.32   7.345%   $172.0955   $172.10   $172.10   $172.10  
  Purchase #5 $49.55   7.211%   $53.1231   $53.12   $53.10   $53.10  
  Purchase #6 $22.56   3.213%   $23.2849   $23.28   $23.30   $23.30  
  Purchase #7 $246.98   8.381%   $267.6794   $267.68   $267.70   $267.70  
  7 purchase totals = $1,145.63       $1,263.5084   $1,263.51   $1,263.55   $1,263.50