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 $46.56   10.143%   $51.2826   $51.28   $51.30   $51.30  
  Purchase #2 $160.85   6.431%   $171.1943   $171.19   $171.20   $171.20  
  Purchase #3 $179.93   12.471%   $202.3691   $202.37   $202.35   $202.40  
  Purchase #4 $158.57   5.565%   $167.3944   $167.39   $167.40   $167.40  
  Purchase #5 $88.36   8.759%   $96.0995   $96.10   $96.10   $96.10  
  Purchase #6 $55.51   10.167%   $61.1537   $61.15   $61.15   $61.20  
  Purchase #7 $204.93   6.120%   $217.4717   $217.47   $217.45   $217.50  
  7 purchase totals = $894.71       $966.9653   $966.95   $966.95   $967.10