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 $66.74   3.547%   $69.1073   $69.11   $69.10   $69.10  
  Purchase #2 $193.39   9.542%   $211.8433   $211.84   $211.85   $211.80  
  Purchase #3 $50.96   11.357%   $56.7475   $56.75   $56.75   $56.70  
  Purchase #4 $108.59   12.232%   $121.8727   $121.87   $121.85   $121.90  
  Purchase #5 $132.65   11.615%   $148.0573   $148.06   $148.05   $148.10  
  Purchase #6 $250.76   10.597%   $277.333   $277.33   $277.35   $277.30  
  Purchase #7 $181.87   7.210%   $194.9828   $194.98   $195.00   $195.00  
  7 purchase totals = $984.96       $1,079.9439   $1,079.94   $1,079.95   $1,079.90