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 $232.93   13.230%   $263.7466   $263.75   $263.75   $263.70  
  Purchase #2 $118.73   12.868%   $134.0082   $134.01   $134.00   $134.00  
  Purchase #3 $184.48   11.529%   $205.7487   $205.75   $205.75   $205.70  
  Purchase #4 $243.33   9.260%   $265.8624   $265.86   $265.85   $265.90  
  Purchase #5 $15.74   11.294%   $17.5177   $17.52   $17.50   $17.50  
  Purchase #6 $15.88   10.546%   $17.5547   $17.55   $17.55   $17.60  
  Purchase #7 $181.92   7.628%   $195.7969   $195.80   $195.80   $195.80  
  7 purchase totals = $993.01       $1,100.2352   $1,100.24   $1,100.20   $1,100.20