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 $95.40   7.612%   $102.6618   $102.66   $102.65   $102.70  
  Purchase #2 $201.73   7.239%   $216.3332   $216.33   $216.35   $216.30  
  Purchase #3 $148.74   5.482%   $156.8939   $156.89   $156.90   $156.90  
  Purchase #4 $37.42   4.265%   $39.016   $39.02   $39.00   $39.00  
  Purchase #5 $212.29   10.379%   $234.3236   $234.32   $234.30   $234.30  
  Purchase #6 $49.64   11.834%   $55.5144   $55.51   $55.50   $55.50  
  Purchase #7 $161.57   12.171%   $181.2347   $181.23   $181.25   $181.20  
  7 purchase totals = $906.79       $985.9776   $985.96   $985.95   $985.90