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 $58.89   7.563%   $63.3439   $63.34   $63.35   $63.30  
  Purchase #2 $189.40   7.474%   $203.5558   $203.56   $203.55   $203.60  
  Purchase #3 $156.53   5.872%   $165.7214   $165.72   $165.70   $165.70  
  Purchase #4 $40.57   7.481%   $43.605   $43.61   $43.60   $43.60  
  Purchase #5 $157.50   7.330%   $169.0448   $169.04   $169.05   $169.00  
  Purchase #6 $241.53   12.124%   $270.8131   $270.81   $270.80   $270.80  
  Purchase #7 $149.58   8.151%   $161.7723   $161.77   $161.75   $161.80  
  7 purchase totals = $994.00       $1,077.8563   $1,077.85   $1,077.80   $1,077.80