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 $213.92   6.278%   $227.3499   $227.35   $227.35   $227.30  
  Purchase #2 $221.97   9.588%   $243.2525   $243.25   $243.25   $243.30  
  Purchase #3 $72.29   11.447%   $80.565   $80.57   $80.55   $80.60  
  Purchase #4 $190.37   5.612%   $201.0536   $201.05   $201.05   $201.10  
  Purchase #5 $31.61   12.582%   $35.5872   $35.59   $35.60   $35.60  
  Purchase #6 $56.95   6.871%   $60.863   $60.86   $60.85   $60.90  
  Purchase #7 $173.88   6.849%   $185.789   $185.79   $185.80   $185.80  
  7 purchase totals = $960.99       $1,034.4602   $1,034.46   $1,034.45   $1,034.60