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 $232.82   9.180%   $254.1929   $254.19   $254.20   $254.20  
  Purchase #2 $210.65   8.614%   $228.7954   $228.80   $228.80   $228.80  
  Purchase #3 $17.94   5.368%   $18.903   $18.90   $18.90   $18.90  
  Purchase #4 $152.97   8.160%   $165.4524   $165.45   $165.45   $165.50  
  Purchase #5 $247.46   3.826%   $256.9278   $256.93   $256.95   $256.90  
  Purchase #6 $86.97   13.234%   $98.4796   $98.48   $98.50   $98.50  
  Purchase #7 $171.43   3.156%   $176.8403   $176.84   $176.85   $176.80  
  7 purchase totals = $1,120.24       $1,199.5914   $1,199.59   $1,199.65   $1,199.60