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 $205.33   10.477%   $226.8424   $226.84   $226.85   $226.80  
  Purchase #2 $223.80   13.751%   $254.5747   $254.57   $254.55   $254.60  
  Purchase #3 $171.27   3.255%   $176.8448   $176.84   $176.85   $176.80  
  Purchase #4 $43.91   8.265%   $47.5392   $47.54   $47.55   $47.50  
  Purchase #5 $131.93   11.302%   $146.8407   $146.84   $146.85   $146.80  
  Purchase #6 $180.64   12.471%   $203.1676   $203.17   $203.15   $203.20  
  Purchase #7 $127.90   4.277%   $133.3703   $133.37   $133.35   $133.40  
  7 purchase totals = $1,084.78       $1,189.1797   $1,189.17   $1,189.15   $1,189.10