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 $187.47   10.134%   $206.4682   $206.47   $206.45   $206.50  
  Purchase #2 $143.96   8.478%   $156.1649   $156.16   $156.15   $156.20  
  Purchase #3 $34.37   13.270%   $38.9309   $38.93   $38.95   $38.90  
  Purchase #4 $110.27   6.823%   $117.7937   $117.79   $117.80   $117.80  
  Purchase #5 $64.80   9.398%   $70.8899   $70.89   $70.90   $70.90  
  Purchase #6 $139.52   11.401%   $155.4267   $155.43   $155.45   $155.40  
  Purchase #7 $22.73   6.736%   $24.2611   $24.26   $24.25   $24.30  
  7 purchase totals = $703.12       $769.9354   $769.93   $769.95   $770.00