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 $59.50   7.533%   $63.9821   $63.98   $64.00   $64.00  
  Purchase #2 $86.75   5.279%   $91.3295   $91.33   $91.35   $91.30  
  Purchase #3 $102.58   10.352%   $113.1991   $113.20   $113.20   $113.20  
  Purchase #4 $26.35   13.241%   $29.839   $29.84   $29.85   $29.80  
  Purchase #5 $178.90   7.865%   $192.9705   $192.97   $192.95   $193.00  
  Purchase #6 $245.55   13.871%   $279.6102   $279.61   $279.60   $279.60  
  Purchase #7 $218.87   5.257%   $230.376   $230.38   $230.40   $230.40  
  7 purchase totals = $918.50       $1,001.3064   $1,001.31   $1,001.35   $1,001.30