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 $183.70   11.790%   $205.3582   $205.36   $205.35   $205.40  
  Purchase #2 $56.92   6.389%   $60.5566   $60.56   $60.55   $60.60  
  Purchase #3 $162.57   6.793%   $173.6134   $173.61   $173.60   $173.60  
  Purchase #4 $228.27   9.137%   $249.127   $249.13   $249.15   $249.10  
  Purchase #5 $160.84   12.587%   $181.0849   $181.08   $181.10   $181.10  
  Purchase #6 $172.98   6.315%   $183.9037   $183.90   $183.90   $183.90  
  Purchase #7 $20.38   12.804%   $22.9895   $22.99   $23.00   $23.00  
  7 purchase totals = $985.66       $1,076.6333   $1,076.63   $1,076.65   $1,076.70