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 $130.92   5.558%   $138.1965   $138.20   $138.20   $138.20  
  Purchase #2 $224.96   13.326%   $254.9382   $254.94   $254.95   $254.90  
  Purchase #3 $46.26   3.682%   $47.9633   $47.96   $47.95   $48.00  
  Purchase #4 $243.51   4.141%   $253.5937   $253.59   $253.60   $253.60  
  Purchase #5 $194.87   13.828%   $221.8166   $221.82   $221.80   $221.80  
  Purchase #6 $175.71   3.120%   $181.1922   $181.19   $181.20   $181.20  
  Purchase #7 $47.74   12.713%   $53.8092   $53.81   $53.80   $53.80  
  7 purchase totals = $1,063.97       $1,151.5097   $1,151.51   $1,151.50   $1,151.50