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 $89.57   5.374%   $94.3835   $94.38   $94.40   $94.40  
  Purchase #2 $54.93   7.343%   $58.9635   $58.96   $58.95   $59.00  
  Purchase #3 $231.80   9.548%   $253.9323   $253.93   $253.95   $253.90  
  Purchase #4 $204.54   12.819%   $230.76   $230.76   $230.75   $230.80  
  Purchase #5 $133.40   8.772%   $145.1018   $145.10   $145.10   $145.10  
  Purchase #6 $187.29   6.171%   $198.8477   $198.85   $198.85   $198.80  
  Purchase #7 $69.34   10.269%   $76.4605   $76.46   $76.45   $76.50  
  7 purchase totals = $970.87       $1,058.4493   $1,058.44   $1,058.45   $1,058.50