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 $84.48   13.173%   $95.6086   $95.61   $95.60   $95.60  
  Purchase #2 $199.53   6.521%   $212.5414   $212.54   $212.55   $212.50  
  Purchase #3 $102.40   8.190%   $110.7866   $110.79   $110.80   $110.80  
  Purchase #4 $202.30   10.566%   $223.675   $223.68   $223.70   $223.70  
  Purchase #5 $137.50   13.271%   $155.7476   $155.75   $155.75   $155.70  
  Purchase #6 $78.68   7.254%   $84.3874   $84.39   $84.40   $84.40  
  Purchase #7 $190.36   3.130%   $196.3183   $196.32   $196.30   $196.30  
  7 purchase totals = $995.25       $1,079.0649   $1,079.08   $1,079.10   $1,079.00