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 $89.98   5.259%   $94.712   $94.71   $94.70   $94.70  
  Purchase #2 $145.85   3.436%   $150.8614   $150.86   $150.85   $150.90  
  Purchase #3 $46.79   7.118%   $50.1205   $50.12   $50.10   $50.10  
  Purchase #4 $53.32   8.697%   $57.9572   $57.96   $57.95   $58.00  
  Purchase #5 $153.91   13.699%   $174.9941   $174.99   $175.00   $175.00  
  Purchase #6 $205.83   11.823%   $230.1653   $230.17   $230.15   $230.20  
  Purchase #7 $7.64   7.818%   $8.2373   $8.24   $8.25   $8.20  
  7 purchase totals = $703.32       $767.0478   $767.05   $767.00   $767.10