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 $205.69   13.369%   $233.1887   $233.19   $233.20   $233.20  
  Purchase #2 $111.44   7.116%   $119.3701   $119.37   $119.35   $119.40  
  Purchase #3 $121.94   10.364%   $134.5779   $134.58   $134.60   $134.60  
  Purchase #4 $135.35   8.600%   $146.9901   $146.99   $147.00   $147.00  
  Purchase #5 $235.64   7.234%   $252.6862   $252.69   $252.70   $252.70  
  Purchase #6 $23.31   6.548%   $24.8363   $24.84   $24.85   $24.80  
  Purchase #7 $223.91   10.627%   $247.7049   $247.70   $247.70   $247.70  
  7 purchase totals = $1,057.28       $1,159.3542   $1,159.36   $1,159.40   $1,159.40