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 $61.45   12.502%   $69.1325   $69.13   $69.15   $69.10  
  Purchase #2 $193.94   13.280%   $219.6952   $219.70   $219.70   $219.70  
  Purchase #3 $195.39   4.474%   $204.1317   $204.13   $204.15   $204.10  
  Purchase #4 $128.63   13.368%   $145.8253   $145.83   $145.85   $145.80  
  Purchase #5 $131.47   6.809%   $140.4218   $140.42   $140.40   $140.40  
  Purchase #6 $161.95   12.584%   $182.3298   $182.33   $182.35   $182.30  
  Purchase #7 $44.32   12.580%   $49.8955   $49.90   $49.90   $49.90  
  7 purchase totals = $917.15       $1,011.4318   $1,011.44   $1,011.50   $1,011.30