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 $154.29   8.252%   $167.022   $167.02   $167.00   $167.00  
  Purchase #2 $212.97   6.589%   $227.0026   $227.00   $227.00   $227.00  
  Purchase #3 $178.91   12.280%   $200.8801   $200.88   $200.90   $200.90  
  Purchase #4 $201.27   4.402%   $210.1299   $210.13   $210.15   $210.10  
  Purchase #5 $229.77   6.195%   $244.0043   $244.00   $244.00   $244.00  
  Purchase #6 $26.56   10.242%   $29.2803   $29.28   $29.30   $29.30  
  Purchase #7 $174.61   6.731%   $186.363   $186.36   $186.35   $186.40  
  7 purchase totals = $1,178.38       $1,264.6822   $1,264.67   $1,264.70   $1,264.70