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 $43.90   5.592%   $46.3549   $46.35   $46.35   $46.40  
  Purchase #2 $241.40   9.795%   $265.0451   $265.05   $265.05   $265.00  
  Purchase #3 $9.54   11.556%   $10.6424   $10.64   $10.65   $10.60  
  Purchase #4 $5.81   3.531%   $6.0152   $6.02   $6.00   $6.00  
  Purchase #5 $148.88   12.378%   $167.3084   $167.31   $167.30   $167.30  
  Purchase #6 $80.74   12.664%   $90.9649   $90.96   $90.95   $91.00  
  Purchase #7 $212.33   13.695%   $241.4086   $241.41   $241.40   $241.40  
  7 purchase totals = $742.60       $827.7395   $827.74   $827.70   $827.70