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 $158.96   9.856%   $174.6271   $174.63   $174.65   $174.60  
  Purchase #2 $223.50   4.551%   $233.6715   $233.67   $233.65   $233.70  
  Purchase #3 $165.59   7.709%   $178.3553   $178.36   $178.35   $178.40  
  Purchase #4 $66.39   9.705%   $72.8331   $72.83   $72.85   $72.80  
  Purchase #5 $117.82   7.734%   $126.9322   $126.93   $126.95   $126.90  
  Purchase #6 $163.87   3.867%   $170.2069   $170.21   $170.20   $170.20  
  Purchase #7 $102.70   13.609%   $116.6764   $116.68   $116.70   $116.70  
  7 purchase totals = $998.83       $1,073.3025   $1,073.31   $1,073.35   $1,073.30