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 $222.77   8.483%   $241.6676   $241.67   $241.65   $241.70  
  Purchase #2 $72.66   11.759%   $81.2041   $81.20   $81.20   $81.20  
  Purchase #3 $150.66   11.485%   $167.9633   $167.96   $167.95   $168.00  
  Purchase #4 $160.98   3.387%   $166.4324   $166.43   $166.45   $166.40  
  Purchase #5 $29.31   12.589%   $32.9998   $33.00   $33.00   $33.00  
  Purchase #6 $171.97   11.723%   $192.13   $192.13   $192.15   $192.10  
  Purchase #7 $119.27   8.156%   $128.9977   $129.00   $129.00   $129.00  
  7 purchase totals = $927.62       $1,011.3949   $1,011.39   $1,011.40   $1,011.40