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 $94.45   8.256%   $102.2478   $102.25   $102.25   $102.20  
  Purchase #2 $144.45   10.832%   $160.0968   $160.10   $160.10   $160.10  
  Purchase #3 $211.48   6.769%   $225.7951   $225.80   $225.80   $225.80  
  Purchase #4 $176.57   4.484%   $184.4874   $184.49   $184.50   $184.50  
  Purchase #5 $195.51   9.264%   $213.622   $213.62   $213.60   $213.60  
  Purchase #6 $239.87   4.160%   $249.8486   $249.85   $249.85   $249.80  
  Purchase #7 $31.71   11.657%   $35.4064   $35.41   $35.40   $35.40  
  7 purchase totals = $1,094.04       $1,171.5041   $1,171.52   $1,171.50   $1,171.40