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 $193.66   6.117%   $205.5062   $205.51   $205.50   $205.50  
  Purchase #2 $58.64   5.251%   $61.7192   $61.72   $61.70   $61.70  
  Purchase #3 $105.79   11.372%   $117.8204   $117.82   $117.80   $117.80  
  Purchase #4 $77.39   13.838%   $88.0992   $88.10   $88.10   $88.10  
  Purchase #5 $188.32   7.789%   $202.9882   $202.99   $203.00   $203.00  
  Purchase #6 $161.27   9.841%   $177.1406   $177.14   $177.15   $177.10  
  Purchase #7 $230.31   6.328%   $244.884   $244.88   $244.90   $244.90  
  7 purchase totals = $1,015.38       $1,098.1578   $1,098.16   $1,098.15   $1,098.10