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 $248.71   9.208%   $271.6112   $271.61   $271.60   $271.60  
  Purchase #2 $40.60   11.689%   $45.3457   $45.35   $45.35   $45.30  
  Purchase #3 $26.77   7.559%   $28.7935   $28.79   $28.80   $28.80  
  Purchase #4 $190.88   11.399%   $212.6384   $212.64   $212.65   $212.60  
  Purchase #5 $175.28   3.326%   $181.1098   $181.11   $181.10   $181.10  
  Purchase #6 $241.79   9.474%   $264.6972   $264.70   $264.70   $264.70  
  Purchase #7 $62.79   10.424%   $69.3352   $69.34   $69.35   $69.30  
  7 purchase totals = $986.82       $1,073.5310   $1,073.54   $1,073.55   $1,073.40