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 $247.47   11.352%   $275.5628   $275.56   $275.55   $275.60  
  Purchase #2 $72.43   5.478%   $76.3977   $76.40   $76.40   $76.40  
  Purchase #3 $94.87   6.130%   $100.6855   $100.69   $100.70   $100.70  
  Purchase #4 $69.64   7.742%   $75.0315   $75.03   $75.05   $75.00  
  Purchase #5 $206.26   8.754%   $224.316   $224.32   $224.30   $224.30  
  Purchase #6 $22.64   13.807%   $25.7659   $25.77   $25.75   $25.80  
  Purchase #7 $248.98   11.182%   $276.8209   $276.82   $276.80   $276.80  
  7 purchase totals = $962.29       $1,054.5803   $1,054.59   $1,054.55   $1,054.60