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 $73.97   13.470%   $83.9338   $83.93   $83.95   $83.90  
  Purchase #2 $217.94   11.494%   $242.99   $242.99   $243.00   $243.00  
  Purchase #3 $113.74   10.506%   $125.6895   $125.69   $125.70   $125.70  
  Purchase #4 $189.93   3.288%   $196.1749   $196.17   $196.15   $196.20  
  Purchase #5 $153.90   11.502%   $171.6016   $171.60   $171.60   $171.60  
  Purchase #6 $127.47   8.300%   $138.05   $138.05   $138.05   $138.10  
  Purchase #7 $71.83   3.851%   $74.5962   $74.60   $74.60   $74.60  
  7 purchase totals = $948.78       $1,033.0360   $1,033.03   $1,033.05   $1,033.10