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 $76.53   10.457%   $84.5327   $84.53   $84.55   $84.50  
  Purchase #2 $191.54   8.509%   $207.8381   $207.84   $207.85   $207.80  
  Purchase #3 $199.32   12.325%   $223.8862   $223.89   $223.90   $223.90  
  Purchase #4 $216.35   9.154%   $236.1547   $236.15   $236.15   $236.20  
  Purchase #5 $147.54   10.481%   $163.0037   $163.00   $163.00   $163.00  
  Purchase #6 $224.97   8.834%   $244.8438   $244.84   $244.85   $244.80  
  Purchase #7 $184.73   10.215%   $203.6002   $203.60   $203.60   $203.60  
  7 purchase totals = $1,240.98       $1,363.8594   $1,363.85   $1,363.90   $1,363.80