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 $213.81   6.140%   $226.9379   $226.94   $226.95   $226.90  
  Purchase #2 $88.81   11.102%   $98.6697   $98.67   $98.65   $98.70  
  Purchase #3 $182.57   11.721%   $203.969   $203.97   $203.95   $204.00  
  Purchase #4 $26.30   4.807%   $27.5642   $27.56   $27.55   $27.60  
  Purchase #5 $160.83   13.815%   $183.0487   $183.05   $183.05   $183.00  
  Purchase #6 $152.47   8.378%   $165.2439   $165.24   $165.25   $165.20  
  Purchase #7 $106.29   10.792%   $117.7608   $117.76   $117.75   $117.80  
  7 purchase totals = $931.08       $1,023.1942   $1,023.19   $1,023.15   $1,023.20