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 $228.46   5.607%   $241.2698   $241.27   $241.25   $241.30  
  Purchase #2 $230.96   9.281%   $252.3954   $252.40   $252.40   $252.40  
  Purchase #3 $126.85   8.580%   $137.7337   $137.73   $137.75   $137.70  
  Purchase #4 $56.50   7.615%   $60.8025   $60.80   $60.80   $60.80  
  Purchase #5 $103.40   9.264%   $112.979   $112.98   $113.00   $113.00  
  Purchase #6 $192.52   5.406%   $202.9276   $202.93   $202.95   $202.90  
  Purchase #7 $239.34   11.649%   $267.2207   $267.22   $267.20   $267.20  
  7 purchase totals = $1,178.03       $1,275.3287   $1,275.33   $1,275.35   $1,275.30