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 $52.68   9.824%   $57.8553   $57.86   $57.85   $57.90  
  Purchase #2 $150.41   5.714%   $159.0044   $159.00   $159.00   $159.00  
  Purchase #3 $214.25   6.468%   $228.1077   $228.11   $228.10   $228.10  
  Purchase #4 $212.72   7.871%   $229.4632   $229.46   $229.45   $229.50  
  Purchase #5 $69.33   11.117%   $77.0374   $77.04   $77.05   $77.00  
  Purchase #6 $32.42   3.769%   $33.6419   $33.64   $33.65   $33.60  
  Purchase #7 $62.74   7.488%   $67.438   $67.44   $67.45   $67.40  
  7 purchase totals = $794.55       $852.5479   $852.55   $852.55   $852.50