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 $177.39   13.384%   $201.1319   $201.13   $201.15   $201.10  
  Purchase #2 $29.57   12.216%   $33.1823   $33.18   $33.20   $33.20  
  Purchase #3 $43.55   8.548%   $47.2727   $47.27   $47.25   $47.30  
  Purchase #4 $238.61   12.143%   $267.5844   $267.58   $267.60   $267.60  
  Purchase #5 $211.27   10.874%   $234.2435   $234.24   $234.25   $234.20  
  Purchase #6 $71.47   10.279%   $78.8164   $78.82   $78.80   $78.80  
  Purchase #7 $31.40   4.323%   $32.7574   $32.76   $32.75   $32.80  
  7 purchase totals = $803.26       $894.9886   $894.98   $895.00   $895.00