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 $162.84   8.197%   $176.188   $176.19   $176.20   $176.20  
  Purchase #2 $53.41   6.717%   $56.9975   $57.00   $57.00   $57.00  
  Purchase #3 $230.88   9.345%   $252.4557   $252.46   $252.45   $252.50  
  Purchase #4 $83.82   6.838%   $89.5516   $89.55   $89.55   $89.60  
  Purchase #5 $60.37   3.147%   $62.2698   $62.27   $62.25   $62.30  
  Purchase #6 $112.77   7.575%   $121.3123   $121.31   $121.30   $121.30  
  Purchase #7 $234.38   8.312%   $253.8617   $253.86   $253.85   $253.90  
  7 purchase totals = $938.47       $1,012.6366   $1,012.64   $1,012.60   $1,012.80