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 $193.88   3.677%   $201.009   $201.01   $201.00   $201.00  
  Purchase #2 $179.98   7.179%   $192.9008   $192.90   $192.90   $192.90  
  Purchase #3 $173.43   5.475%   $182.9253   $182.93   $182.95   $182.90  
  Purchase #4 $237.98   3.744%   $246.89   $246.89   $246.90   $246.90  
  Purchase #5 $64.65   9.579%   $70.8428   $70.84   $70.85   $70.80  
  Purchase #6 $38.51   3.357%   $39.8028   $39.80   $39.80   $39.80  
  Purchase #7 $50.55   7.447%   $54.3145   $54.31   $54.30   $54.30  
  7 purchase totals = $938.98       $988.6852   $988.68   $988.70   $988.60