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 $65.84   3.683%   $68.2649   $68.26   $68.25   $68.30  
  Purchase #2 $180.45   8.338%   $195.4959   $195.50   $195.50   $195.50  
  Purchase #3 $67.79   6.668%   $72.3102   $72.31   $72.30   $72.30  
  Purchase #4 $214.91   6.108%   $228.0367   $228.04   $228.05   $228.00  
  Purchase #5 $16.57   6.636%   $17.6696   $17.67   $17.65   $17.70  
  Purchase #6 $153.28   4.672%   $160.4412   $160.44   $160.45   $160.40  
  Purchase #7 $200.60   13.691%   $228.0641   $228.06   $228.05   $228.10  
  7 purchase totals = $899.44       $970.2826   $970.28   $970.25   $970.30