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 $159.65   9.557%   $174.9078   $174.91   $174.90   $174.90  
  Purchase #2 $51.93   8.473%   $56.33   $56.33   $56.35   $56.30  
  Purchase #3 $236.30   4.229%   $246.2931   $246.29   $246.30   $246.30  
  Purchase #4 $58.86   9.205%   $64.2781   $64.28   $64.30   $64.30  
  Purchase #5 $235.36   4.547%   $246.0618   $246.06   $246.05   $246.10  
  Purchase #6 $117.91   13.504%   $133.8326   $133.83   $133.85   $133.80  
  Purchase #7 $88.33   8.594%   $95.9211   $95.92   $95.90   $95.90  
  7 purchase totals = $948.34       $1,017.6245   $1,017.62   $1,017.65   $1,017.60