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 $183.34   6.158%   $194.6301   $194.63   $194.65   $194.60  
  Purchase #2 $202.99   6.567%   $216.3204   $216.32   $216.30   $216.30  
  Purchase #3 $5.67   5.524%   $5.9832   $5.98   $6.00   $6.00  
  Purchase #4 $239.52   3.146%   $247.0553   $247.06   $247.05   $247.10  
  Purchase #5 $233.58   12.610%   $263.0344   $263.03   $263.05   $263.00  
  Purchase #6 $234.44   9.485%   $256.6766   $256.68   $256.70   $256.70  
  Purchase #7 $70.54   12.466%   $79.3335   $79.33   $79.35   $79.30  
  7 purchase totals = $1,170.08       $1,263.0335   $1,263.03   $1,263.10   $1,263.00