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 $96.59   8.378%   $104.6823   $104.68   $104.70   $104.70  
  Purchase #2 $81.27   7.613%   $87.4571   $87.46   $87.45   $87.50  
  Purchase #3 $41.79   7.145%   $44.7759   $44.78   $44.80   $44.80  
  Purchase #4 $243.48   7.838%   $262.564   $262.56   $262.55   $262.60  
  Purchase #5 $147.39   11.246%   $163.9655   $163.97   $163.95   $164.00  
  Purchase #6 $114.51   7.404%   $122.9883   $122.99   $123.00   $123.00  
  Purchase #7 $219.85   6.504%   $234.149   $234.15   $234.15   $234.10  
  7 purchase totals = $944.88       $1,020.5821   $1,020.59   $1,020.60   $1,020.70