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 $109.55   11.457%   $122.1011   $122.10   $122.10   $122.10  
  Purchase #2 $131.33   4.569%   $137.3305   $137.33   $137.35   $137.30  
  Purchase #3 $112.59   4.442%   $117.5912   $117.59   $117.60   $117.60  
  Purchase #4 $206.95   12.515%   $232.8498   $232.85   $232.85   $232.80  
  Purchase #5 $226.90   9.244%   $247.8746   $247.87   $247.85   $247.90  
  Purchase #6 $23.37   13.290%   $26.4759   $26.48   $26.50   $26.50  
  Purchase #7 $147.47   13.259%   $167.023   $167.02   $167.00   $167.00  
  7 purchase totals = $958.16       $1,051.2461   $1,051.24   $1,051.25   $1,051.20