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 $214.73   9.359%   $234.8266   $234.83   $234.85   $234.80  
  Purchase #2 $197.25   3.387%   $203.9309   $203.93   $203.95   $203.90  
  Purchase #3 $192.75   9.435%   $210.936   $210.94   $210.95   $210.90  
  Purchase #4 $50.98   13.398%   $57.8103   $57.81   $57.80   $57.80  
  Purchase #5 $26.26   5.315%   $27.6557   $27.66   $27.65   $27.70  
  Purchase #6 $10.31   10.301%   $11.372   $11.37   $11.35   $11.40  
  Purchase #7 $232.96   11.528%   $259.8156   $259.82   $259.80   $259.80  
  7 purchase totals = $925.24       $1,006.3471   $1,006.36   $1,006.35   $1,006.30