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 $249.44   13.688%   $283.5833   $283.58   $283.60   $283.60  
  Purchase #2 $183.31   12.405%   $206.0496   $206.05   $206.05   $206.00  
  Purchase #3 $76.95   7.416%   $82.6566   $82.66   $82.65   $82.70  
  Purchase #4 $92.87   3.121%   $95.7685   $95.77   $95.75   $95.80  
  Purchase #5 $96.52   7.558%   $103.815   $103.82   $103.80   $103.80  
  Purchase #6 $59.35   5.378%   $62.5418   $62.54   $62.55   $62.50  
  Purchase #7 $182.32   9.715%   $200.0324   $200.03   $200.05   $200.00  
  7 purchase totals = $940.76       $1,034.4472   $1,034.45   $1,034.45   $1,034.40