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 $52.63   13.206%   $59.5803   $59.58   $59.60   $59.60  
  Purchase #2 $92.83   6.291%   $98.6699   $98.67   $98.65   $98.70  
  Purchase #3 $91.98   12.649%   $103.6146   $103.61   $103.60   $103.60  
  Purchase #4 $44.68   11.473%   $49.8061   $49.81   $49.80   $49.80  
  Purchase #5 $225.59   8.240%   $244.1786   $244.18   $244.20   $244.20  
  Purchase #6 $198.90   12.208%   $223.1817   $223.18   $223.20   $223.20  
  Purchase #7 $220.78   13.690%   $251.0048   $251.00   $251.00   $251.00  
  7 purchase totals = $927.39       $1,030.0360   $1,030.03   $1,030.05   $1,030.10