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 $32.99   5.270%   $34.7286   $34.73   $34.75   $34.70  
  Purchase #2 $47.75   13.227%   $54.0659   $54.07   $54.05   $54.10  
  Purchase #3 $69.26   13.623%   $78.6953   $78.70   $78.70   $78.70  
  Purchase #4 $154.40   13.256%   $174.8673   $174.87   $174.85   $174.90  
  Purchase #5 $107.49   10.420%   $118.6905   $118.69   $118.70   $118.70  
  Purchase #6 $154.92   9.596%   $169.7861   $169.79   $169.80   $169.80  
  Purchase #7 $128.67   7.558%   $138.3949   $138.39   $138.40   $138.40  
  7 purchase totals = $695.48       $769.2286   $769.24   $769.25   $769.30