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 $61.58   11.219%   $68.4887   $68.49   $68.50   $68.50  
  Purchase #2 $90.90   9.236%   $99.2955   $99.30   $99.30   $99.30  
  Purchase #3 $202.98   3.796%   $210.6851   $210.69   $210.70   $210.70  
  Purchase #4 $92.96   11.124%   $103.3009   $103.30   $103.30   $103.30  
  Purchase #5 $72.59   5.224%   $76.3821   $76.38   $76.40   $76.40  
  Purchase #6 $174.52   13.125%   $197.4258   $197.43   $197.45   $197.40  
  Purchase #7 $204.79   7.522%   $220.1943   $220.19   $220.20   $220.20  
  7 purchase totals = $900.32       $975.7724   $975.78   $975.85   $975.80