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 $66.30   11.290%   $73.7853   $73.79   $73.80   $73.80  
  Purchase #2 $230.41   6.471%   $245.3198   $245.32   $245.30   $245.30  
  Purchase #3 $235.54   7.673%   $253.613   $253.61   $253.60   $253.60  
  Purchase #4 $102.93   4.826%   $107.8974   $107.90   $107.90   $107.90  
  Purchase #5 $244.35   8.864%   $266.0092   $266.01   $266.00   $266.00  
  Purchase #6 $205.30   9.460%   $224.7214   $224.72   $224.70   $224.70  
  Purchase #7 $180.61   13.647%   $205.2578   $205.26   $205.25   $205.30  
  7 purchase totals = $1,265.44       $1,376.6039   $1,376.61   $1,376.55   $1,376.60