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 $86.86   6.212%   $92.2557   $92.26   $92.25   $92.30  
  Purchase #2 $151.31   11.183%   $168.231   $168.23   $168.25   $168.20  
  Purchase #3 $47.60   9.362%   $52.0563   $52.06   $52.05   $52.10  
  Purchase #4 $210.37   4.589%   $220.0239   $220.02   $220.00   $220.00  
  Purchase #5 $86.76   13.374%   $98.3633   $98.36   $98.35   $98.40  
  Purchase #6 $204.99   8.713%   $222.8508   $222.85   $222.85   $222.90  
  Purchase #7 $152.94   4.447%   $159.7412   $159.74   $159.75   $159.70  
  7 purchase totals = $940.83       $1,013.5222   $1,013.52   $1,013.50   $1,013.60