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 $122.27   3.174%   $126.1508   $126.15   $126.15   $126.20  
  Purchase #2 $63.71   3.591%   $65.9978   $66.00   $66.00   $66.00  
  Purchase #3 $159.50   7.529%   $171.5088   $171.51   $171.50   $171.50  
  Purchase #4 $213.41   11.431%   $237.8049   $237.80   $237.80   $237.80  
  Purchase #5 $204.87   10.627%   $226.6415   $226.64   $226.65   $226.60  
  Purchase #6 $148.54   12.792%   $167.5412   $167.54   $167.55   $167.50  
  Purchase #7 $244.37   3.412%   $252.7079   $252.71   $252.70   $252.70  
  7 purchase totals = $1,156.67       $1,248.3529   $1,248.35   $1,248.35   $1,248.30