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 $92.44   3.588%   $95.7567   $95.76   $95.75   $95.80  
  Purchase #2 $82.67   9.134%   $90.2211   $90.22   $90.20   $90.20  
  Purchase #3 $223.69   10.167%   $246.4326   $246.43   $246.45   $246.40  
  Purchase #4 $192.65   12.484%   $216.7004   $216.70   $216.70   $216.70  
  Purchase #5 $61.59   11.824%   $68.8724   $68.87   $68.85   $68.90  
  Purchase #6 $150.58   4.791%   $157.7943   $157.79   $157.80   $157.80  
  Purchase #7 $135.55   5.635%   $143.1882   $143.19   $143.20   $143.20  
  7 purchase totals = $939.17       $1,018.9657   $1,018.96   $1,018.95   $1,019.00