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 $230.62   6.559%   $245.7464   $245.75   $245.75   $245.70  
  Purchase #2 $221.83   8.596%   $240.8985   $240.90   $240.90   $240.90  
  Purchase #3 $189.99   11.327%   $211.5102   $211.51   $211.50   $211.50  
  Purchase #4 $225.33   3.278%   $232.7163   $232.72   $232.70   $232.70  
  Purchase #5 $220.79   11.221%   $245.5648   $245.56   $245.55   $245.60  
  Purchase #6 $95.93   13.632%   $109.0072   $109.01   $109.00   $109.00  
  Purchase #7 $92.79   8.316%   $100.5064   $100.51   $100.50   $100.50  
  7 purchase totals = $1,277.28       $1,385.9498   $1,385.96   $1,385.90   $1,385.90