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 $118.90   3.151%   $122.6465   $122.65   $122.65   $122.60  
  Purchase #2 $174.94   12.591%   $196.9667   $196.97   $196.95   $197.00  
  Purchase #3 $59.78   3.179%   $61.6804   $61.68   $61.70   $61.70  
  Purchase #4 $155.58   3.332%   $160.7639   $160.76   $160.75   $160.80  
  Purchase #5 $118.49   11.443%   $132.0488   $132.05   $132.05   $132.00  
  Purchase #6 $142.85   10.586%   $157.9721   $157.97   $157.95   $158.00  
  Purchase #7 $223.46   13.175%   $252.9009   $252.90   $252.90   $252.90  
  7 purchase totals = $994.00       $1,084.9793   $1,084.98   $1,084.95   $1,085.00