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 $68.79   12.381%   $77.3069   $77.31   $77.30   $77.30  
  Purchase #2 $199.46   13.141%   $225.671   $225.67   $225.65   $225.70  
  Purchase #3 $113.33   11.233%   $126.0604   $126.06   $126.05   $126.10  
  Purchase #4 $92.69   10.732%   $102.6375   $102.64   $102.65   $102.60  
  Purchase #5 $163.60   9.553%   $179.2287   $179.23   $179.25   $179.20  
  Purchase #6 $186.92   10.618%   $206.7672   $206.77   $206.75   $206.80  
  Purchase #7 $91.52   3.563%   $94.7809   $94.78   $94.80   $94.80  
  7 purchase totals = $916.31       $1,012.4526   $1,012.46   $1,012.45   $1,012.50