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 $146.37   12.744%   $165.0234   $165.02   $165.00   $165.00  
  Purchase #2 $208.79   11.545%   $232.8948   $232.89   $232.90   $232.90  
  Purchase #3 $147.96   4.322%   $154.3548   $154.35   $154.35   $154.40  
  Purchase #4 $180.93   3.503%   $187.268   $187.27   $187.25   $187.30  
  Purchase #5 $131.92   4.297%   $137.5886   $137.59   $137.60   $137.60  
  Purchase #6 $117.41   7.763%   $126.5245   $126.52   $126.50   $126.50  
  Purchase #7 $220.42   3.667%   $228.5028   $228.50   $228.50   $228.50  
  7 purchase totals = $1,153.80       $1,232.1569   $1,232.14   $1,232.10   $1,232.20