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 $245.56   10.481%   $271.2971   $271.30   $271.30   $271.30  
  Purchase #2 $210.75   6.219%   $223.8565   $223.86   $223.85   $223.90  
  Purchase #3 $51.29   9.717%   $56.2738   $56.27   $56.25   $56.30  
  Purchase #4 $20.30   10.605%   $22.4528   $22.45   $22.45   $22.50  
  Purchase #5 $216.97   13.501%   $246.2631   $246.26   $246.25   $246.30  
  Purchase #6 $61.66   9.669%   $67.6219   $67.62   $67.60   $67.60  
  Purchase #7 $201.82   13.222%   $228.5046   $228.50   $228.50   $228.50  
  7 purchase totals = $1,008.35       $1,116.2698   $1,116.26   $1,116.20   $1,116.40