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 $191.46   5.316%   $201.638   $201.64   $201.65   $201.60  
  Purchase #2 $55.56   5.458%   $58.5925   $58.59   $58.60   $58.60  
  Purchase #3 $213.48   3.768%   $221.5239   $221.52   $221.50   $221.50  
  Purchase #4 $73.89   8.287%   $80.0133   $80.01   $80.00   $80.00  
  Purchase #5 $240.36   5.562%   $253.7288   $253.73   $253.75   $253.70  
  Purchase #6 $80.60   12.812%   $90.9265   $90.93   $90.95   $90.90  
  Purchase #7 $106.36   11.310%   $118.3893   $118.39   $118.40   $118.40  
  7 purchase totals = $961.71       $1,024.8123   $1,024.81   $1,024.85   $1,024.70