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 $56.67   7.240%   $60.7729   $60.77   $60.75   $60.80  
  Purchase #2 $91.65   8.630%   $99.5594   $99.56   $99.55   $99.60  
  Purchase #3 $59.34   3.789%   $61.5884   $61.59   $61.60   $61.60  
  Purchase #4 $203.78   8.306%   $220.706   $220.71   $220.70   $220.70  
  Purchase #5 $175.66   9.288%   $191.9753   $191.98   $192.00   $192.00  
  Purchase #6 $107.58   5.674%   $113.6841   $113.68   $113.70   $113.70  
  Purchase #7 $137.61   9.112%   $150.149   $150.15   $150.15   $150.10  
  7 purchase totals = $832.29       $898.4351   $898.44   $898.45   $898.50