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 $46.98   12.664%   $52.9295   $52.93   $52.95   $52.90  
  Purchase #2 $34.96   9.692%   $38.3483   $38.35   $38.35   $38.30  
  Purchase #3 $52.54   9.244%   $57.3968   $57.40   $57.40   $57.40  
  Purchase #4 $207.44   5.689%   $219.2413   $219.24   $219.25   $219.20  
  Purchase #5 $75.81   11.475%   $84.5092   $84.51   $84.50   $84.50  
  Purchase #6 $205.58   8.505%   $223.0646   $223.06   $223.05   $223.10  
  Purchase #7 $76.87   5.262%   $80.9149   $80.91   $80.90   $80.90  
  7 purchase totals = $700.18       $756.4046   $756.40   $756.40   $756.30