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 $205.76   11.665%   $229.7619   $229.76   $229.75   $229.80  
  Purchase #2 $212.60   9.146%   $232.0444   $232.04   $232.05   $232.00  
  Purchase #3 $25.59   3.546%   $26.4974   $26.50   $26.50   $26.50  
  Purchase #4 $154.32   4.849%   $161.803   $161.80   $161.80   $161.80  
  Purchase #5 $181.57   9.601%   $199.0025   $199.00   $199.00   $199.00  
  Purchase #6 $60.80   13.494%   $69.0044   $69.00   $69.00   $69.00  
  Purchase #7 $211.76   11.236%   $235.5534   $235.55   $235.55   $235.60  
  7 purchase totals = $1,052.40       $1,153.6670   $1,153.65   $1,153.65   $1,153.70