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 $11.43   13.585%   $12.9828   $12.98   $13.00   $13.00  
  Purchase #2 $134.69   5.412%   $141.9794   $141.98   $142.00   $142.00  
  Purchase #3 $167.28   9.331%   $182.8889   $182.89   $182.90   $182.90  
  Purchase #4 $206.34   9.798%   $226.5572   $226.56   $226.55   $226.60  
  Purchase #5 $217.29   12.133%   $243.6538   $243.65   $243.65   $243.70  
  Purchase #6 $158.68   4.201%   $165.3461   $165.35   $165.35   $165.30  
  Purchase #7 $93.36   3.166%   $96.3158   $96.32   $96.30   $96.30  
  7 purchase totals = $989.07       $1,069.7240   $1,069.73   $1,069.75   $1,069.80