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 $58.78   6.632%   $62.6783   $62.68   $62.70   $62.70  
  Purchase #2 $186.64   4.705%   $195.4214   $195.42   $195.40   $195.40  
  Purchase #3 $245.84   7.761%   $264.9196   $264.92   $264.90   $264.90  
  Purchase #4 $87.85   5.443%   $92.6317   $92.63   $92.65   $92.60  
  Purchase #5 $178.94   13.332%   $202.7963   $202.80   $202.80   $202.80  
  Purchase #6 $235.67   13.829%   $268.2608   $268.26   $268.25   $268.30  
  Purchase #7 $11.44   12.488%   $12.8686   $12.87   $12.85   $12.90  
  7 purchase totals = $1,005.16       $1,099.5767   $1,099.58   $1,099.55   $1,099.60