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 $211.32   7.298%   $226.7421   $226.74   $226.75   $226.70  
  Purchase #2 $191.58   6.424%   $203.8871   $203.89   $203.90   $203.90  
  Purchase #3 $213.36   9.503%   $233.6356   $233.64   $233.65   $233.60  
  Purchase #4 $212.89   13.580%   $241.8005   $241.80   $241.80   $241.80  
  Purchase #5 $57.63   4.246%   $60.077   $60.08   $60.10   $60.10  
  Purchase #6 $44.78   5.771%   $47.3643   $47.36   $47.35   $47.40  
  Purchase #7 $20.25   9.753%   $22.225   $22.23   $22.25   $22.20  
  7 purchase totals = $951.81       $1,035.7316   $1,035.74   $1,035.80   $1,035.70