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 $232.53   13.420%   $263.7355   $263.74   $263.75   $263.70  
  Purchase #2 $156.65   5.612%   $165.4412   $165.44   $165.45   $165.40  
  Purchase #3 $13.97   13.529%   $15.86   $15.86   $15.85   $15.90  
  Purchase #4 $160.88   12.610%   $181.167   $181.17   $181.15   $181.20  
  Purchase #5 $118.47   10.212%   $130.5682   $130.57   $130.55   $130.60  
  Purchase #6 $150.83   12.104%   $169.0865   $169.09   $169.10   $169.10  
  Purchase #7 $94.70   10.838%   $104.9636   $104.96   $104.95   $105.00  
  7 purchase totals = $928.03       $1,030.8220   $1,030.83   $1,030.80   $1,030.90