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 $61.42   8.316%   $66.5277   $66.53   $66.55   $66.50  
  Purchase #2 $146.49   6.477%   $155.9782   $155.98   $156.00   $156.00  
  Purchase #3 $237.72   12.361%   $267.1046   $267.10   $267.10   $267.10  
  Purchase #4 $192.95   6.474%   $205.4416   $205.44   $205.45   $205.40  
  Purchase #5 $181.97   10.858%   $201.7283   $201.73   $201.75   $201.70  
  Purchase #6 $10.37   8.784%   $11.2809   $11.28   $11.30   $11.30  
  Purchase #7 $238.26   13.864%   $271.2924   $271.29   $271.30   $271.30  
  7 purchase totals = $1,069.18       $1,179.3537   $1,179.35   $1,179.45   $1,179.30