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 $152.25   9.716%   $167.0426   $167.04   $167.05   $167.00  
  Purchase #2 $214.73   10.653%   $237.6052   $237.61   $237.60   $237.60  
  Purchase #3 $226.34   13.336%   $256.5247   $256.52   $256.50   $256.50  
  Purchase #4 $77.85   10.184%   $85.7782   $85.78   $85.80   $85.80  
  Purchase #5 $175.73   10.361%   $193.9374   $193.94   $193.95   $193.90  
  Purchase #6 $220.39   10.351%   $243.2026   $243.20   $243.20   $243.20  
  Purchase #7 $72.57   13.142%   $82.1071   $82.11   $82.10   $82.10  
  7 purchase totals = $1,139.86       $1,266.1978   $1,266.20   $1,266.20   $1,266.10