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 $186.28   6.164%   $197.7623   $197.76   $197.75   $197.80  
  Purchase #2 $82.92   12.818%   $93.5487   $93.55   $93.55   $93.50  
  Purchase #3 $123.74   10.452%   $136.6733   $136.67   $136.65   $136.70  
  Purchase #4 $168.37   4.581%   $176.083   $176.08   $176.10   $176.10  
  Purchase #5 $192.56   7.847%   $207.6702   $207.67   $207.65   $207.70  
  Purchase #6 $59.70   4.653%   $62.4778   $62.48   $62.50   $62.50  
  Purchase #7 $183.89   10.510%   $203.2168   $203.22   $203.20   $203.20  
  7 purchase totals = $997.46       $1,077.4321   $1,077.43   $1,077.40   $1,077.50