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 $178.79   10.809%   $198.1154   $198.12   $198.10   $198.10  
  Purchase #2 $113.38   10.148%   $124.8858   $124.89   $124.90   $124.90  
  Purchase #3 $174.42   11.192%   $193.9411   $193.94   $193.95   $193.90  
  Purchase #4 $146.92   9.190%   $160.4219   $160.42   $160.40   $160.40  
  Purchase #5 $134.83   5.211%   $141.856   $141.86   $141.85   $141.90  
  Purchase #6 $66.46   3.295%   $68.6499   $68.65   $68.65   $68.60  
  Purchase #7 $122.29   10.529%   $135.1659   $135.17   $135.15   $135.20  
  7 purchase totals = $937.09       $1,023.0360   $1,023.05   $1,023.00   $1,023.00