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 $64.74   5.251%   $68.1395   $68.14   $68.15   $68.10  
  Purchase #2 $243.38   4.170%   $253.5289   $253.53   $253.55   $253.50  
  Purchase #3 $94.99   12.705%   $107.0585   $107.06   $107.05   $107.10  
  Purchase #4 $134.83   5.817%   $142.6731   $142.67   $142.65   $142.70  
  Purchase #5 $212.62   11.557%   $237.1925   $237.19   $237.20   $237.20  
  Purchase #6 $38.47   13.679%   $43.7323   $43.73   $43.75   $43.70  
  Purchase #7 $186.31   7.222%   $199.7653   $199.77   $199.75   $199.80  
  7 purchase totals = $975.34       $1,052.0901   $1,052.09   $1,052.10   $1,052.10