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 $120.86   13.541%   $137.2257   $137.23   $137.25   $137.20  
  Purchase #2 $247.56   9.820%   $271.8704   $271.87   $271.85   $271.90  
  Purchase #3 $78.52   6.159%   $83.356   $83.36   $83.35   $83.40  
  Purchase #4 $234.79   8.228%   $254.1085   $254.11   $254.10   $254.10  
  Purchase #5 $55.45   8.560%   $60.1965   $60.20   $60.20   $60.20  
  Purchase #6 $165.95   8.559%   $180.1537   $180.15   $180.15   $180.20  
  Purchase #7 $116.93   8.861%   $127.2912   $127.29   $127.30   $127.30  
  7 purchase totals = $1,020.06       $1,114.2020   $1,114.21   $1,114.20   $1,114.30