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 $247.28   7.861%   $266.7187   $266.72   $266.70   $266.70  
  Purchase #2 $228.73   7.397%   $245.6492   $245.65   $245.65   $245.60  
  Purchase #3 $131.78   12.231%   $147.898   $147.90   $147.90   $147.90  
  Purchase #4 $82.39   4.761%   $86.3126   $86.31   $86.30   $86.30  
  Purchase #5 $121.92   8.363%   $132.1162   $132.12   $132.10   $132.10  
  Purchase #6 $27.83   10.465%   $30.7424   $30.74   $30.75   $30.70  
  Purchase #7 $145.72   3.759%   $151.1976   $151.20   $151.20   $151.20  
  7 purchase totals = $985.65       $1,060.6347   $1,060.64   $1,060.60   $1,060.50