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 $150.82   6.715%   $160.9476   $160.95   $160.95   $160.90  
  Purchase #2 $229.69   10.125%   $252.9461   $252.95   $252.95   $252.90  
  Purchase #3 $99.70   11.209%   $110.8754   $110.88   $110.90   $110.90  
  Purchase #4 $131.63   10.427%   $145.3551   $145.36   $145.35   $145.40  
  Purchase #5 $47.81   12.489%   $53.781   $53.78   $53.80   $53.80  
  Purchase #6 $131.62   5.364%   $138.6801   $138.68   $138.70   $138.70  
  Purchase #7 $173.79   12.255%   $195.088   $195.09   $195.10   $195.10  
  7 purchase totals = $965.06       $1,057.6733   $1,057.69   $1,057.75   $1,057.70