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 $110.78   10.616%   $122.5404   $122.54   $122.55   $122.50  
  Purchase #2 $236.53   13.163%   $267.6644   $267.66   $267.65   $267.70  
  Purchase #3 $216.58   5.459%   $228.4031   $228.40   $228.40   $228.40  
  Purchase #4 $114.33   13.344%   $129.5862   $129.59   $129.60   $129.60  
  Purchase #5 $80.47   4.759%   $84.2996   $84.30   $84.30   $84.30  
  Purchase #6 $93.39   5.258%   $98.3004   $98.30   $98.30   $98.30  
  Purchase #7 $215.54   6.719%   $230.0221   $230.02   $230.00   $230.00  
  7 purchase totals = $1,067.62       $1,160.8162   $1,160.81   $1,160.80   $1,160.80