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 $61.49   3.564%   $63.6815   $63.68   $63.70   $63.70  
  Purchase #2 $81.26   9.620%   $89.0772   $89.08   $89.10   $89.10  
  Purchase #3 $116.45   10.313%   $128.4595   $128.46   $128.45   $128.50  
  Purchase #4 $55.50   6.244%   $58.9654   $58.97   $58.95   $59.00  
  Purchase #5 $99.92   6.765%   $106.6796   $106.68   $106.70   $106.70  
  Purchase #6 $178.69   8.424%   $193.7428   $193.74   $193.75   $193.70  
  Purchase #7 $222.93   3.180%   $230.0192   $230.02   $230.00   $230.00  
  7 purchase totals = $816.24       $870.6252   $870.63   $870.65   $870.70