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 $106.70   11.862%   $119.3568   $119.36   $119.35   $119.40  
  Purchase #2 $226.47   7.342%   $243.0974   $243.10   $243.10   $243.10  
  Purchase #3 $161.86   3.761%   $167.9476   $167.95   $167.95   $167.90  
  Purchase #4 $219.54   8.726%   $238.6971   $238.70   $238.70   $238.70  
  Purchase #5 $231.78   9.784%   $254.4574   $254.46   $254.45   $254.50  
  Purchase #6 $143.58   5.553%   $151.553   $151.55   $151.55   $151.60  
  Purchase #7 $222.84   4.811%   $233.5608   $233.56   $233.55   $233.60  
  7 purchase totals = $1,312.77       $1,408.6701   $1,408.68   $1,408.65   $1,408.80