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 $69.60   8.262%   $75.3504   $75.35   $75.35   $75.40  
  Purchase #2 $244.51   9.408%   $267.5135   $267.51   $267.50   $267.50  
  Purchase #3 $179.66   7.528%   $193.1848   $193.18   $193.20   $193.20  
  Purchase #4 $58.56   12.590%   $65.9327   $65.93   $65.95   $65.90  
  Purchase #5 $204.95   3.567%   $212.2606   $212.26   $212.25   $212.30  
  Purchase #6 $106.48   3.867%   $110.5976   $110.60   $110.60   $110.60  
  Purchase #7 $119.87   9.493%   $131.2493   $131.25   $131.25   $131.20  
  7 purchase totals = $983.63       $1,056.0889   $1,056.08   $1,056.10   $1,056.10