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 $160.73   10.197%   $177.1196   $177.12   $177.10   $177.10  
  Purchase #2 $206.71   4.812%   $216.6569   $216.66   $216.65   $216.70  
  Purchase #3 $86.74   13.534%   $98.4794   $98.48   $98.50   $98.50  
  Purchase #4 $84.30   13.611%   $95.7741   $95.77   $95.75   $95.80  
  Purchase #5 $186.93   8.260%   $202.3704   $202.37   $202.35   $202.40  
  Purchase #6 $169.37   5.410%   $178.5329   $178.53   $178.55   $178.50  
  Purchase #7 $238.51   10.771%   $264.1999   $264.20   $264.20   $264.20  
  7 purchase totals = $1,133.29       $1,233.1332   $1,233.13   $1,233.10   $1,233.20