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 $68.41   13.501%   $77.646   $77.65   $77.65   $77.60  
  Purchase #2 $177.85   13.379%   $201.6446   $201.64   $201.65   $201.60  
  Purchase #3 $193.82   4.643%   $202.8191   $202.82   $202.80   $202.80  
  Purchase #4 $25.79   3.183%   $26.6109   $26.61   $26.60   $26.60  
  Purchase #5 $209.93   6.224%   $222.996   $223.00   $223.00   $223.00  
  Purchase #6 $76.57   5.472%   $80.7599   $80.76   $80.75   $80.80  
  Purchase #7 $182.84   8.498%   $198.3777   $198.38   $198.40   $198.40  
  7 purchase totals = $935.21       $1,010.8542   $1,010.86   $1,010.85   $1,010.80