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 $164.43   7.103%   $176.1095   $176.11   $176.10   $176.10  
  Purchase #2 $62.49   13.157%   $70.7118   $70.71   $70.70   $70.70  
  Purchase #3 $59.75   10.451%   $65.9945   $65.99   $66.00   $66.00  
  Purchase #4 $123.98   9.129%   $135.2981   $135.30   $135.30   $135.30  
  Purchase #5 $244.85   7.457%   $263.1085   $263.11   $263.10   $263.10  
  Purchase #6 $194.61   8.761%   $211.6598   $211.66   $211.65   $211.70  
  Purchase #7 $142.36   9.770%   $156.2686   $156.27   $156.25   $156.30  
  7 purchase totals = $992.47       $1,079.1508   $1,079.15   $1,079.10   $1,079.20