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 $61.61   11.753%   $68.851   $68.85   $68.85   $68.90  
  Purchase #2 $89.34   12.689%   $100.6764   $100.68   $100.70   $100.70  
  Purchase #3 $45.87   11.674%   $51.2249   $51.22   $51.20   $51.20  
  Purchase #4 $166.45   9.482%   $182.2328   $182.23   $182.25   $182.20  
  Purchase #5 $51.62   4.184%   $53.7798   $53.78   $53.80   $53.80  
  Purchase #6 $121.52   13.807%   $138.2983   $138.30   $138.30   $138.30  
  Purchase #7 $145.44   12.763%   $164.0025   $164.00   $164.00   $164.00  
  7 purchase totals = $681.85       $759.0657   $759.06   $759.10   $759.10