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 $54.85   12.873%   $61.9108   $61.91   $61.90   $61.90  
  Purchase #2 $64.92   3.225%   $67.0137   $67.01   $67.00   $67.00  
  Purchase #3 $102.65   4.245%   $107.0075   $107.01   $107.00   $107.00  
  Purchase #4 $105.51   12.146%   $118.3252   $118.33   $118.35   $118.30  
  Purchase #5 $109.95   4.443%   $114.8351   $114.84   $114.85   $114.80  
  Purchase #6 $166.42   4.591%   $174.0603   $174.06   $174.05   $174.10  
  Purchase #7 $168.30   3.808%   $174.7089   $174.71   $174.70   $174.70  
  7 purchase totals = $772.60       $817.8615   $817.87   $817.85   $817.80