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 $108.49   4.615%   $113.4968   $113.50   $113.50   $113.50  
  Purchase #2 $27.84   6.689%   $29.7022   $29.70   $29.70   $29.70  
  Purchase #3 $125.28   7.695%   $134.9203   $134.92   $134.90   $134.90  
  Purchase #4 $124.28   4.676%   $130.0913   $130.09   $130.10   $130.10  
  Purchase #5 $159.77   9.395%   $174.7804   $174.78   $174.80   $174.80  
  Purchase #6 $211.50   7.703%   $227.7918   $227.79   $227.80   $227.80  
  Purchase #7 $216.45   6.761%   $231.0842   $231.08   $231.10   $231.10  
  7 purchase totals = $973.61       $1,041.8670   $1,041.86   $1,041.90   $1,041.90