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 $87.86   10.252%   $96.8674   $96.87   $96.85   $96.90  
  Purchase #2 $147.92   13.519%   $167.9173   $167.92   $167.90   $167.90  
  Purchase #3 $121.61   10.397%   $134.2538   $134.25   $134.25   $134.30  
  Purchase #4 $189.88   8.834%   $206.654   $206.65   $206.65   $206.70  
  Purchase #5 $49.40   12.614%   $55.6313   $55.63   $55.65   $55.60  
  Purchase #6 $244.74   4.579%   $255.9466   $255.95   $255.95   $255.90  
  Purchase #7 $184.94   10.540%   $204.4327   $204.43   $204.45   $204.40  
  7 purchase totals = $1,026.35       $1,121.7031   $1,121.70   $1,121.70   $1,121.70