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 $86.83   7.454%   $93.3023   $93.30   $93.30   $93.30  
  Purchase #2 $93.50   9.520%   $102.4012   $102.40   $102.40   $102.40  
  Purchase #3 $227.66   8.392%   $246.7652   $246.77   $246.75   $246.80  
  Purchase #4 $200.75   9.761%   $220.3452   $220.35   $220.35   $220.30  
  Purchase #5 $144.80   8.186%   $156.6533   $156.65   $156.65   $156.70  
  Purchase #6 $25.44   5.691%   $26.8878   $26.89   $26.90   $26.90  
  Purchase #7 $152.94   11.812%   $171.0053   $171.01   $171.00   $171.00  
  7 purchase totals = $931.92       $1,017.3603   $1,017.37   $1,017.35   $1,017.40