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 $162.34   5.651%   $171.5138   $171.51   $171.50   $171.50  
  Purchase #2 $56.54   4.107%   $58.8621   $58.86   $58.85   $58.90  
  Purchase #3 $203.80   3.245%   $210.4133   $210.41   $210.40   $210.40  
  Purchase #4 $77.41   7.853%   $83.489   $83.49   $83.50   $83.50  
  Purchase #5 $155.63   3.536%   $161.1331   $161.13   $161.15   $161.10  
  Purchase #6 $196.42   4.816%   $205.8796   $205.88   $205.90   $205.90  
  Purchase #7 $231.63   4.336%   $241.6735   $241.67   $241.65   $241.70  
  7 purchase totals = $1,083.77       $1,132.9644   $1,132.95   $1,132.95   $1,133.00