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 $101.29   9.622%   $111.0361   $111.04   $111.05   $111.00  
  Purchase #2 $237.37   4.558%   $248.1893   $248.19   $248.20   $248.20  
  Purchase #3 $34.89   13.439%   $39.5789   $39.58   $39.60   $39.60  
  Purchase #4 $113.37   11.108%   $125.9631   $125.96   $125.95   $126.00  
  Purchase #5 $217.43   10.614%   $240.508   $240.51   $240.50   $240.50  
  Purchase #6 $169.59   10.146%   $186.7966   $186.80   $186.80   $186.80  
  Purchase #7 $98.46   6.216%   $104.5803   $104.58   $104.60   $104.60  
  7 purchase totals = $972.40       $1,056.6523   $1,056.66   $1,056.70   $1,056.70