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 $59.27   5.125%   $62.3076   $62.31   $62.30   $62.30  
  Purchase #2 $208.62   7.661%   $224.6024   $224.60   $224.60   $224.60  
  Purchase #3 $23.81   9.623%   $26.1012   $26.10   $26.10   $26.10  
  Purchase #4 $32.68   12.632%   $36.8081   $36.81   $36.80   $36.80  
  Purchase #5 $220.88   4.476%   $230.7666   $230.77   $230.75   $230.80  
  Purchase #6 $49.83   7.646%   $53.64   $53.64   $53.65   $53.60  
  Purchase #7 $189.66   12.837%   $214.0067   $214.01   $214.00   $214.00  
  7 purchase totals = $784.75       $848.2326   $848.24   $848.20   $848.20