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 $244.30   13.386%   $277.002   $277.00   $277.00   $277.00  
  Purchase #2 $230.46   9.667%   $252.7386   $252.74   $252.75   $252.70  
  Purchase #3 $124.79   6.410%   $132.789   $132.79   $132.80   $132.80  
  Purchase #4 $24.97   6.840%   $26.6779   $26.68   $26.70   $26.70  
  Purchase #5 $62.93   3.387%   $65.0614   $65.06   $65.05   $65.10  
  Purchase #6 $23.83   6.478%   $25.3737   $25.37   $25.35   $25.40  
  Purchase #7 $211.83   12.666%   $238.6604   $238.66   $238.65   $238.70  
  7 purchase totals = $923.11       $1,018.3030   $1,018.30   $1,018.30   $1,018.40