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 $56.29   12.301%   $63.2142   $63.21   $63.20   $63.20  
  Purchase #2 $171.88   6.383%   $182.8511   $182.85   $182.85   $182.90  
  Purchase #3 $82.51   8.802%   $89.7725   $89.77   $89.75   $89.80  
  Purchase #4 $115.80   9.111%   $126.3505   $126.35   $126.35   $126.40  
  Purchase #5 $194.46   5.218%   $204.6069   $204.61   $204.60   $204.60  
  Purchase #6 $45.36   9.274%   $49.5667   $49.57   $49.55   $49.60  
  Purchase #7 $56.48   7.594%   $60.7691   $60.77   $60.75   $60.80  
  7 purchase totals = $722.78       $777.1310   $777.13   $777.05   $777.30