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 $151.34   10.671%   $167.4895   $167.49   $167.50   $167.50  
  Purchase #2 $118.93   6.382%   $126.5201   $126.52   $126.50   $126.50  
  Purchase #3 $147.99   10.685%   $163.8027   $163.80   $163.80   $163.80  
  Purchase #4 $220.35   3.794%   $228.7101   $228.71   $228.70   $228.70  
  Purchase #5 $180.44   9.201%   $197.0423   $197.04   $197.05   $197.00  
  Purchase #6 $238.33   11.415%   $265.5354   $265.54   $265.55   $265.50  
  Purchase #7 $56.34   12.363%   $63.3053   $63.31   $63.30   $63.30  
  7 purchase totals = $1,113.72       $1,212.4054   $1,212.41   $1,212.40   $1,212.30