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 $213.62   8.597%   $231.9849   $231.98   $232.00   $232.00  
  Purchase #2 $87.40   6.536%   $93.1125   $93.11   $93.10   $93.10  
  Purchase #3 $101.65   5.869%   $107.6158   $107.62   $107.60   $107.60  
  Purchase #4 $113.97   8.770%   $123.9652   $123.97   $123.95   $124.00  
  Purchase #5 $158.47   10.117%   $174.5024   $174.50   $174.50   $174.50  
  Purchase #6 $203.46   6.636%   $216.9616   $216.96   $216.95   $217.00  
  Purchase #7 $80.46   9.120%   $87.798   $87.80   $87.80   $87.80  
  7 purchase totals = $959.03       $1,035.9404   $1,035.94   $1,035.90   $1,036.00