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 $71.57   3.148%   $73.823   $73.82   $73.80   $73.80  
  Purchase #2 $181.66   6.537%   $193.5351   $193.54   $193.55   $193.50  
  Purchase #3 $39.93   8.717%   $43.4107   $43.41   $43.40   $43.40  
  Purchase #4 $103.97   13.306%   $117.8042   $117.80   $117.80   $117.80  
  Purchase #5 $146.32   9.425%   $160.1107   $160.11   $160.10   $160.10  
  Purchase #6 $234.91   6.576%   $250.3577   $250.36   $250.35   $250.40  
  Purchase #7 $69.48   11.479%   $77.4556   $77.46   $77.45   $77.50  
  7 purchase totals = $847.84       $916.4970   $916.50   $916.45   $916.50