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 $175.94   12.641%   $198.1806   $198.18   $198.20   $198.20  
  Purchase #2 $43.68   11.805%   $48.8364   $48.84   $48.85   $48.80  
  Purchase #3 $117.43   7.802%   $126.5919   $126.59   $126.60   $126.60  
  Purchase #4 $151.74   6.598%   $161.7518   $161.75   $161.75   $161.80  
  Purchase #5 $241.53   11.438%   $269.1562   $269.16   $269.15   $269.20  
  Purchase #6 $159.59   6.319%   $169.6745   $169.67   $169.65   $169.70  
  Purchase #7 $238.63   5.731%   $252.3059   $252.31   $252.30   $252.30  
  7 purchase totals = $1,128.54       $1,226.4973   $1,226.50   $1,226.50   $1,226.60