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 $142.31   8.156%   $153.9168   $153.92   $153.90   $153.90  
  Purchase #2 $63.70   3.579%   $65.9798   $65.98   $66.00   $66.00  
  Purchase #3 $211.90   12.310%   $237.9849   $237.98   $238.00   $238.00  
  Purchase #4 $139.29   12.260%   $156.367   $156.37   $156.35   $156.40  
  Purchase #5 $145.29   11.257%   $161.6453   $161.65   $161.65   $161.60  
  Purchase #6 $58.93   4.204%   $61.4074   $61.41   $61.40   $61.40  
  Purchase #7 $149.27   9.805%   $163.9059   $163.91   $163.90   $163.90  
  7 purchase totals = $910.69       $1,001.2071   $1,001.22   $1,001.20   $1,001.20