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 $70.89   5.818%   $75.0144   $75.01   $75.00   $75.00  
  Purchase #2 $203.55   11.388%   $226.7303   $226.73   $226.75   $226.70  
  Purchase #3 $188.43   6.497%   $200.6723   $200.67   $200.65   $200.70  
  Purchase #4 $159.76   10.154%   $175.982   $175.98   $176.00   $176.00  
  Purchase #5 $132.41   4.585%   $138.481   $138.48   $138.50   $138.50  
  Purchase #6 $82.88   9.361%   $90.6384   $90.64   $90.65   $90.60  
  Purchase #7 $16.49   12.570%   $18.5628   $18.56   $18.55   $18.60  
  7 purchase totals = $854.41       $926.0812   $926.07   $926.10   $926.10