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 $249.41   6.661%   $266.0232   $266.02   $266.00   $266.00  
  Purchase #2 $104.80   3.507%   $108.4753   $108.48   $108.50   $108.50  
  Purchase #3 $235.62   3.439%   $243.723   $243.72   $243.70   $243.70  
  Purchase #4 $77.34   13.694%   $87.9309   $87.93   $87.95   $87.90  
  Purchase #5 $132.78   9.611%   $145.5415   $145.54   $145.55   $145.50  
  Purchase #6 $50.26   4.594%   $52.5689   $52.57   $52.55   $52.60  
  Purchase #7 $106.81   3.419%   $110.4618   $110.46   $110.45   $110.50  
  7 purchase totals = $957.02       $1,014.7246   $1,014.72   $1,014.70   $1,014.70