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 $96.47   5.692%   $101.9611   $101.96   $101.95   $102.00  
  Purchase #2 $145.49   4.373%   $151.8523   $151.85   $151.85   $151.90  
  Purchase #3 $182.65   4.851%   $191.5104   $191.51   $191.50   $191.50  
  Purchase #4 $157.79   8.594%   $171.3505   $171.35   $171.35   $171.40  
  Purchase #5 $134.30   13.203%   $152.0316   $152.03   $152.05   $152.00  
  Purchase #6 $194.31   10.874%   $215.4393   $215.44   $215.45   $215.40  
  Purchase #7 $15.28   7.837%   $16.4775   $16.48   $16.50   $16.50  
  7 purchase totals = $926.29       $1,000.6227   $1,000.62   $1,000.65   $1,000.70