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 $76.71   9.796%   $84.2245   $84.22   $84.20   $84.20  
  Purchase #2 $171.94   9.361%   $188.0353   $188.04   $188.05   $188.00  
  Purchase #3 $113.70   13.837%   $129.4327   $129.43   $129.45   $129.40  
  Purchase #4 $220.81   12.257%   $247.8747   $247.87   $247.85   $247.90  
  Purchase #5 $103.51   3.133%   $106.753   $106.75   $106.75   $106.80  
  Purchase #6 $187.85   5.802%   $198.7491   $198.75   $198.75   $198.70  
  Purchase #7 $67.30   5.520%   $71.015   $71.02   $71.00   $71.00  
  7 purchase totals = $941.82       $1,026.0843   $1,026.08   $1,026.05   $1,026.00