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 $152.47   10.163%   $167.9655   $167.97   $167.95   $168.00  
  Purchase #2 $27.34   7.692%   $29.443   $29.44   $29.45   $29.40  
  Purchase #3 $55.68   7.713%   $59.9746   $59.97   $59.95   $60.00  
  Purchase #4 $207.27   13.787%   $235.8463   $235.85   $235.85   $235.80  
  Purchase #5 $121.25   9.438%   $132.6936   $132.69   $132.70   $132.70  
  Purchase #6 $207.49   12.372%   $233.1607   $233.16   $233.15   $233.20  
  Purchase #7 $137.31   8.842%   $149.451   $149.45   $149.45   $149.50  
  7 purchase totals = $908.81       $1,008.5347   $1,008.53   $1,008.50   $1,008.60