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 $49.35   5.444%   $52.0366   $52.04   $52.05   $52.00  
  Purchase #2 $49.53   12.224%   $55.5845   $55.58   $55.60   $55.60  
  Purchase #3 $31.73   7.358%   $34.0647   $34.06   $34.05   $34.10  
  Purchase #4 $145.37   4.264%   $151.5686   $151.57   $151.55   $151.60  
  Purchase #5 $226.74   11.163%   $252.051   $252.05   $252.05   $252.10  
  Purchase #6 $71.86   13.137%   $81.3002   $81.30   $81.30   $81.30  
  Purchase #7 $125.80   7.754%   $135.5545   $135.55   $135.55   $135.60  
  7 purchase totals = $700.38       $762.1601   $762.15   $762.15   $762.30