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 $29.58   13.506%   $33.5751   $33.58   $33.60   $33.60  
  Purchase #2 $236.79   12.453%   $266.2775   $266.28   $266.30   $266.30  
  Purchase #3 $208.38   11.320%   $231.9686   $231.97   $231.95   $232.00  
  Purchase #4 $40.83   12.606%   $45.977   $45.98   $46.00   $46.00  
  Purchase #5 $32.55   11.674%   $36.3499   $36.35   $36.35   $36.30  
  Purchase #6 $234.88   7.270%   $251.9558   $251.96   $251.95   $252.00  
  Purchase #7 $56.74   3.424%   $58.6828   $58.68   $58.70   $58.70  
  7 purchase totals = $839.75       $924.7867   $924.80   $924.85   $924.90