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 $70.61   4.442%   $73.7465   $73.75   $73.75   $73.70  
  Purchase #2 $181.59   12.622%   $204.5103   $204.51   $204.50   $204.50  
  Purchase #3 $91.98   8.379%   $99.687   $99.69   $99.70   $99.70  
  Purchase #4 $244.98   8.704%   $266.3031   $266.30   $266.30   $266.30  
  Purchase #5 $41.52   7.469%   $44.6211   $44.62   $44.60   $44.60  
  Purchase #6 $194.38   11.276%   $216.2983   $216.30   $216.30   $216.30  
  Purchase #7 $155.46   12.593%   $175.0371   $175.04   $175.05   $175.00  
  7 purchase totals = $980.52       $1,080.2034   $1,080.21   $1,080.20   $1,080.10