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 $204.66   9.320%   $223.7343   $223.73   $223.75   $223.70  
  Purchase #2 $154.83   6.385%   $164.7159   $164.72   $164.70   $164.70  
  Purchase #3 $15.46   10.399%   $17.0677   $17.07   $17.05   $17.10  
  Purchase #4 $111.36   3.612%   $115.3823   $115.38   $115.40   $115.40  
  Purchase #5 $84.46   13.618%   $95.9618   $95.96   $95.95   $96.00  
  Purchase #6 $165.26   6.341%   $175.7391   $175.74   $175.75   $175.70  
  Purchase #7 $211.35   4.425%   $220.7022   $220.70   $220.70   $220.70  
  7 purchase totals = $947.38       $1,013.3033   $1,013.30   $1,013.30   $1,013.30