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 $49.35   11.771%   $55.159   $55.16   $55.15   $55.20  
  Purchase #2 $191.52   9.635%   $209.973   $209.97   $209.95   $210.00  
  Purchase #3 $67.64   13.863%   $77.0169   $77.02   $77.00   $77.00  
  Purchase #4 $168.37   4.554%   $176.0376   $176.04   $176.05   $176.00  
  Purchase #5 $16.84   7.461%   $18.0964   $18.10   $18.10   $18.10  
  Purchase #6 $182.44   12.704%   $205.6172   $205.62   $205.60   $205.60  
  Purchase #7 $120.29   3.867%   $124.9416   $124.94   $124.95   $124.90  
  7 purchase totals = $796.45       $866.8417   $866.85   $866.80   $866.80