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 $245.80   10.443%   $271.4689   $271.47   $271.45   $271.50  
  Purchase #2 $113.36   8.427%   $122.9128   $122.91   $122.90   $122.90  
  Purchase #3 $62.75   5.792%   $66.3845   $66.38   $66.40   $66.40  
  Purchase #4 $200.33   5.152%   $210.651   $210.65   $210.65   $210.70  
  Purchase #5 $108.98   12.611%   $122.7235   $122.72   $122.70   $122.70  
  Purchase #6 $100.28   9.820%   $110.1275   $110.13   $110.15   $110.10  
  Purchase #7 $90.47   6.187%   $96.0674   $96.07   $96.05   $96.10  
  7 purchase totals = $921.97       $1,000.3356   $1,000.33   $1,000.30   $1,000.40