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 $230.59   9.215%   $251.8389   $251.84   $251.85   $251.80  
  Purchase #2 $174.96   10.664%   $193.6177   $193.62   $193.60   $193.60  
  Purchase #3 $24.31   10.596%   $26.8859   $26.89   $26.90   $26.90  
  Purchase #4 $155.66   10.120%   $171.4128   $171.41   $171.40   $171.40  
  Purchase #5 $156.51   6.590%   $166.824   $166.82   $166.80   $166.80  
  Purchase #6 $167.96   6.281%   $178.5096   $178.51   $178.50   $178.50  
  Purchase #7 $41.45   6.446%   $44.1219   $44.12   $44.10   $44.10  
  7 purchase totals = $951.44       $1,033.2108   $1,033.21   $1,033.15   $1,033.10