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 $58.79   4.514%   $61.4438   $61.44   $61.45   $61.40  
  Purchase #2 $213.52   8.871%   $232.4614   $232.46   $232.45   $232.50  
  Purchase #3 $201.79   13.141%   $228.3072   $228.31   $228.30   $228.30  
  Purchase #4 $157.53   10.659%   $174.3211   $174.32   $174.30   $174.30  
  Purchase #5 $39.92   8.386%   $43.2677   $43.27   $43.25   $43.30  
  Purchase #6 $123.84   8.630%   $134.5274   $134.53   $134.55   $134.50  
  Purchase #7 $136.50   8.145%   $147.6179   $147.62   $147.60   $147.60  
  7 purchase totals = $931.89       $1,021.9465   $1,021.95   $1,021.90   $1,021.90