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 $153.85   8.488%   $166.9088   $166.91   $166.90   $166.90  
  Purchase #2 $55.87   4.695%   $58.4931   $58.49   $58.50   $58.50  
  Purchase #3 $245.44   4.199%   $255.746   $255.75   $255.75   $255.70  
  Purchase #4 $247.59   3.404%   $256.018   $256.02   $256.00   $256.00  
  Purchase #5 $55.33   13.187%   $62.6264   $62.63   $62.65   $62.60  
  Purchase #6 $243.72   6.323%   $259.1304   $259.13   $259.15   $259.10  
  Purchase #7 $111.95   9.540%   $122.63   $122.63   $122.65   $122.60  
  7 purchase totals = $1,113.75       $1,181.5527   $1,181.56   $1,181.60   $1,181.40