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 $81.88   12.496%   $92.1117   $92.11   $92.10   $92.10  
  Purchase #2 $168.32   3.331%   $173.9267   $173.93   $173.95   $173.90  
  Purchase #3 $212.59   9.488%   $232.7605   $232.76   $232.75   $232.80  
  Purchase #4 $73.63   7.775%   $79.3547   $79.35   $79.35   $79.40  
  Purchase #5 $249.33   6.503%   $265.5439   $265.54   $265.55   $265.50  
  Purchase #6 $217.51   12.329%   $244.3268   $244.33   $244.35   $244.30  
  Purchase #7 $100.59   3.530%   $104.1408   $104.14   $104.15   $104.10  
  7 purchase totals = $1,103.85       $1,192.1651   $1,192.16   $1,192.20   $1,192.10