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 $210.67   10.204%   $232.1668   $232.17   $232.15   $232.20  
  Purchase #2 $84.58   13.686%   $96.1556   $96.16   $96.15   $96.20  
  Purchase #3 $70.76   5.122%   $74.3843   $74.38   $74.40   $74.40  
  Purchase #4 $176.89   10.260%   $195.0389   $195.04   $195.05   $195.00  
  Purchase #5 $219.92   10.497%   $243.005   $243.01   $243.00   $243.00  
  Purchase #6 $79.98   4.269%   $83.3943   $83.39   $83.40   $83.40  
  Purchase #7 $148.70   3.400%   $153.7558   $153.76   $153.75   $153.80  
  7 purchase totals = $991.50       $1,077.9007   $1,077.91   $1,077.90   $1,078.00