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 $248.80   8.729%   $270.5178   $270.52   $270.50   $270.50  
  Purchase #2 $213.84   7.823%   $230.5687   $230.57   $230.55   $230.60  
  Purchase #3 $238.38   9.432%   $260.864   $260.86   $260.85   $260.90  
  Purchase #4 $226.71   8.149%   $245.1846   $245.18   $245.20   $245.20  
  Purchase #5 $116.38   7.436%   $125.034   $125.03   $125.05   $125.00  
  Purchase #6 $250.37   8.811%   $272.4301   $272.43   $272.45   $272.40  
  Purchase #7 $56.89   9.194%   $62.1205   $62.12   $62.10   $62.10  
  7 purchase totals = $1,351.37       $1,466.7197   $1,466.71   $1,466.70   $1,466.70