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 $84.68   11.794%   $94.6672   $94.67   $94.65   $94.70  
  Purchase #2 $200.87   13.616%   $228.2205   $228.22   $228.20   $228.20  
  Purchase #3 $166.45   9.302%   $181.9332   $181.93   $181.95   $181.90  
  Purchase #4 $127.28   12.257%   $142.8807   $142.88   $142.90   $142.90  
  Purchase #5 $7.43   12.196%   $8.3362   $8.34   $8.35   $8.30  
  Purchase #6 $223.61   9.160%   $244.0927   $244.09   $244.10   $244.10  
  Purchase #7 $162.73   6.129%   $172.7037   $172.70   $172.70   $172.70  
  7 purchase totals = $973.05       $1,072.8342   $1,072.83   $1,072.85   $1,072.80