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 $73.96   3.813%   $76.7801   $76.78   $76.80   $76.80  
  Purchase #2 $227.39   6.264%   $241.6337   $241.63   $241.65   $241.60  
  Purchase #3 $220.95   6.319%   $234.9118   $234.91   $234.90   $234.90  
  Purchase #4 $187.80   11.647%   $209.6731   $209.67   $209.65   $209.70  
  Purchase #5 $26.77   8.273%   $28.9847   $28.98   $29.00   $29.00  
  Purchase #6 $246.58   4.655%   $258.0583   $258.06   $258.05   $258.10  
  Purchase #7 $187.27   11.816%   $209.3978   $209.40   $209.40   $209.40  
  7 purchase totals = $1,170.72       $1,259.4395   $1,259.43   $1,259.45   $1,259.50