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 $195.80   9.402%   $214.2091   $214.21   $214.20   $214.20  
  Purchase #2 $112.37   12.365%   $126.2646   $126.26   $126.25   $126.30  
  Purchase #3 $191.85   7.775%   $206.7663   $206.77   $206.75   $206.80  
  Purchase #4 $213.68   6.406%   $227.3683   $227.37   $227.35   $227.40  
  Purchase #5 $248.65   12.412%   $279.5124   $279.51   $279.50   $279.50  
  Purchase #6 $62.30   5.234%   $65.5608   $65.56   $65.55   $65.60  
  Purchase #7 $243.49   4.731%   $255.0095   $255.01   $255.00   $255.00  
  7 purchase totals = $1,268.14       $1,374.6910   $1,374.69   $1,374.60   $1,374.80