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 $66.31   6.688%   $70.7448   $70.74   $70.75   $70.70  
  Purchase #2 $194.78   3.866%   $202.3102   $202.31   $202.30   $202.30  
  Purchase #3 $44.77   4.111%   $46.6105   $46.61   $46.60   $46.60  
  Purchase #4 $62.48   11.803%   $69.8545   $69.85   $69.85   $69.90  
  Purchase #5 $8.67   9.842%   $9.5233   $9.52   $9.50   $9.50  
  Purchase #6 $151.90   6.251%   $161.3953   $161.40   $161.40   $161.40  
  Purchase #7 $213.88   6.350%   $227.4614   $227.46   $227.45   $227.50  
  7 purchase totals = $742.79       $787.9000   $787.89   $787.85   $787.90