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 $41.78   6.824%   $44.6311   $44.63   $44.65   $44.60  
  Purchase #2 $200.85   13.781%   $228.5291   $228.53   $228.55   $228.50  
  Purchase #3 $226.56   10.703%   $250.8087   $250.81   $250.80   $250.80  
  Purchase #4 $97.86   10.823%   $108.4514   $108.45   $108.45   $108.50  
  Purchase #5 $5.30   13.819%   $6.0324   $6.03   $6.05   $6.00  
  Purchase #6 $191.67   10.806%   $212.3819   $212.38   $212.40   $212.40  
  Purchase #7 $214.42   12.542%   $241.3126   $241.31   $241.30   $241.30  
  7 purchase totals = $978.44       $1,092.1472   $1,092.14   $1,092.20   $1,092.10