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 $214.58   8.173%   $232.1176   $232.12   $232.10   $232.10  
  Purchase #2 $65.54   6.663%   $69.9069   $69.91   $69.90   $69.90  
  Purchase #3 $18.77   11.252%   $20.882   $20.88   $20.90   $20.90  
  Purchase #4 $80.28   8.764%   $87.3157   $87.32   $87.30   $87.30  
  Purchase #5 $78.38   8.266%   $84.8589   $84.86   $84.85   $84.90  
  Purchase #6 $247.72   6.560%   $263.9704   $263.97   $263.95   $264.00  
  Purchase #7 $7.54   4.822%   $7.9036   $7.90   $7.90   $7.90  
  7 purchase totals = $712.81       $766.9551   $766.96   $766.90   $767.00