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 $152.49   8.593%   $165.5935   $165.59   $165.60   $165.60  
  Purchase #2 $246.57   9.869%   $270.904   $270.90   $270.90   $270.90  
  Purchase #3 $188.76   3.325%   $195.0363   $195.04   $195.05   $195.00  
  Purchase #4 $24.92   3.813%   $25.8702   $25.87   $25.85   $25.90  
  Purchase #5 $147.68   8.404%   $160.091   $160.09   $160.10   $160.10  
  Purchase #6 $65.29   12.369%   $73.3657   $73.37   $73.35   $73.40  
  Purchase #7 $34.53   5.211%   $36.3294   $36.33   $36.35   $36.30  
  7 purchase totals = $860.24       $927.1901   $927.19   $927.20   $927.20