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 $121.47   8.246%   $131.4864   $131.49   $131.50   $131.50  
  Purchase #2 $69.58   10.169%   $76.6556   $76.66   $76.65   $76.70  
  Purchase #3 $78.94   7.319%   $84.7176   $84.72   $84.70   $84.70  
  Purchase #4 $62.39   6.232%   $66.2781   $66.28   $66.30   $66.30  
  Purchase #5 $89.57   7.550%   $96.3325   $96.33   $96.35   $96.30  
  Purchase #6 $33.35   13.673%   $37.9099   $37.91   $37.90   $37.90  
  Purchase #7 $200.40   9.761%   $219.961   $219.96   $219.95   $220.00  
  7 purchase totals = $655.70       $713.3411   $713.35   $713.35   $713.40