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 $49.93   8.656%   $54.2519   $54.25   $54.25   $54.30  
  Purchase #2 $16.91   3.170%   $17.446   $17.45   $17.45   $17.40  
  Purchase #3 $190.57   6.703%   $203.3439   $203.34   $203.35   $203.30  
  Purchase #4 $60.50   12.727%   $68.1998   $68.20   $68.20   $68.20  
  Purchase #5 $234.33   12.548%   $263.7337   $263.73   $263.75   $263.70  
  Purchase #6 $217.52   11.497%   $242.5283   $242.53   $242.55   $242.50  
  Purchase #7 $199.97   5.807%   $211.5823   $211.58   $211.60   $211.60  
  7 purchase totals = $969.73       $1,061.0859   $1,061.08   $1,061.15   $1,061.00