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 $38.79   6.569%   $41.3381   $41.34   $41.35   $41.30  
  Purchase #2 $16.86   5.426%   $17.7748   $17.77   $17.75   $17.80  
  Purchase #3 $193.44   9.392%   $211.6079   $211.61   $211.60   $211.60  
  Purchase #4 $204.55   9.499%   $223.9802   $223.98   $224.00   $224.00  
  Purchase #5 $23.54   12.293%   $26.4338   $26.43   $26.45   $26.40  
  Purchase #6 $245.33   12.178%   $275.2063   $275.21   $275.20   $275.20  
  Purchase #7 $154.26   10.634%   $170.664   $170.66   $170.65   $170.70  
  7 purchase totals = $876.77       $967.0051   $967.00   $967.00   $967.00