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 $59.67   6.333%   $63.4489   $63.45   $63.45   $63.40  
  Purchase #2 $38.89   11.365%   $43.3098   $43.31   $43.30   $43.30  
  Purchase #3 $181.72   10.799%   $201.3439   $201.34   $201.35   $201.30  
  Purchase #4 $228.66   7.117%   $244.9337   $244.93   $244.95   $244.90  
  Purchase #5 $89.46   5.807%   $94.6549   $94.65   $94.65   $94.70  
  Purchase #6 $215.93   7.402%   $231.9131   $231.91   $231.90   $231.90  
  Purchase #7 $139.85   5.796%   $147.9557   $147.96   $147.95   $148.00  
  7 purchase totals = $954.18       $1,027.5600   $1,027.55   $1,027.55   $1,027.50