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 $76.53   6.755%   $81.6996   $81.70   $81.70   $81.70  
  Purchase #2 $223.46   8.673%   $242.8407   $242.84   $242.85   $242.80  
  Purchase #3 $160.42   10.418%   $177.1326   $177.13   $177.15   $177.10  
  Purchase #4 $173.42   9.744%   $190.318   $190.32   $190.30   $190.30  
  Purchase #5 $229.29   7.467%   $246.4111   $246.41   $246.40   $246.40  
  Purchase #6 $12.36   3.220%   $12.758   $12.76   $12.75   $12.80  
  Purchase #7 $57.29   5.316%   $60.3355   $60.34   $60.35   $60.30  
  7 purchase totals = $932.77       $1,011.4955   $1,011.50   $1,011.50   $1,011.40