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 $228.44   7.734%   $246.1075   $246.11   $246.10   $246.10  
  Purchase #2 $213.65   12.147%   $239.6021   $239.60   $239.60   $239.60  
  Purchase #3 $119.77   12.447%   $134.6778   $134.68   $134.70   $134.70  
  Purchase #4 $249.52   8.548%   $270.849   $270.85   $270.85   $270.80  
  Purchase #5 $159.91   3.456%   $165.4365   $165.44   $165.45   $165.40  
  Purchase #6 $78.38   12.219%   $87.9573   $87.96   $87.95   $88.00  
  Purchase #7 $152.59   6.176%   $162.014   $162.01   $162.00   $162.00  
  7 purchase totals = $1,202.26       $1,306.6442   $1,306.65   $1,306.65   $1,306.60