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 $197.68   7.701%   $212.9033   $212.90   $212.90   $212.90  
  Purchase #2 $83.84   10.367%   $92.5317   $92.53   $92.55   $92.50  
  Purchase #3 $33.75   8.435%   $36.5968   $36.60   $36.60   $36.60  
  Purchase #4 $218.82   6.734%   $233.5553   $233.56   $233.55   $233.60  
  Purchase #5 $248.81   11.717%   $277.9631   $277.96   $277.95   $278.00  
  Purchase #6 $91.72   11.193%   $101.9862   $101.99   $102.00   $102.00  
  Purchase #7 $135.76   6.874%   $145.0921   $145.09   $145.10   $145.10  
  7 purchase totals = $1,010.38       $1,100.6285   $1,100.63   $1,100.65   $1,100.70