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 $219.57   8.398%   $238.0095   $238.01   $238.00   $238.00  
  Purchase #2 $42.48   3.588%   $44.0042   $44.00   $44.00   $44.00  
  Purchase #3 $230.81   3.833%   $239.6569   $239.66   $239.65   $239.70  
  Purchase #4 $87.57   11.642%   $97.7649   $97.76   $97.75   $97.80  
  Purchase #5 $106.50   8.703%   $115.7687   $115.77   $115.75   $115.80  
  Purchase #6 $201.75   4.528%   $210.8852   $210.89   $210.90   $210.90  
  Purchase #7 $73.94   9.385%   $80.8793   $80.88   $80.90   $80.90  
  7 purchase totals = $962.62       $1,026.9687   $1,026.97   $1,026.95   $1,027.10