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 $62.93   11.626%   $70.2462   $70.25   $70.25   $70.20  
  Purchase #2 $20.96   13.225%   $23.732   $23.73   $23.75   $23.70  
  Purchase #3 $122.80   12.713%   $138.4116   $138.41   $138.40   $138.40  
  Purchase #4 $219.46   8.330%   $237.741   $237.74   $237.75   $237.70  
  Purchase #5 $183.65   11.321%   $204.441   $204.44   $204.45   $204.40  
  Purchase #6 $211.45   7.544%   $227.4018   $227.40   $227.40   $227.40  
  Purchase #7 $171.30   11.710%   $191.3592   $191.36   $191.35   $191.40  
  7 purchase totals = $992.55       $1,093.3328   $1,093.33   $1,093.35   $1,093.20