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 $215.93   12.610%   $243.1588   $243.16   $243.15   $243.20  
  Purchase #2 $221.26   13.343%   $250.7827   $250.78   $250.80   $250.80  
  Purchase #3 $39.99   10.226%   $44.0794   $44.08   $44.10   $44.10  
  Purchase #4 $200.57   11.823%   $224.2834   $224.28   $224.30   $224.30  
  Purchase #5 $44.38   11.719%   $49.5809   $49.58   $49.60   $49.60  
  Purchase #6 $153.57   6.525%   $163.5904   $163.59   $163.60   $163.60  
  Purchase #7 $62.28   12.415%   $70.0121   $70.01   $70.00   $70.00  
  7 purchase totals = $937.98       $1,045.4877   $1,045.48   $1,045.55   $1,045.60