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 $158.74   6.473%   $169.0152   $169.02   $169.00   $169.00  
  Purchase #2 $119.86   9.312%   $131.0214   $131.02   $131.00   $131.00  
  Purchase #3 $61.31   6.351%   $65.2038   $65.20   $65.20   $65.20  
  Purchase #4 $143.93   7.469%   $154.6801   $154.68   $154.70   $154.70  
  Purchase #5 $210.42   10.301%   $232.0954   $232.10   $232.10   $232.10  
  Purchase #6 $213.36   5.609%   $225.3274   $225.33   $225.35   $225.30  
  Purchase #7 $237.76   5.219%   $250.1687   $250.17   $250.15   $250.20  
  7 purchase totals = $1,145.38       $1,227.5120   $1,227.52   $1,227.50   $1,227.50