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 $11.25   6.740%   $12.0083   $12.01   $12.00   $12.00  
  Purchase #2 $61.76   6.848%   $65.9893   $65.99   $66.00   $66.00  
  Purchase #3 $167.51   13.834%   $190.6833   $190.68   $190.70   $190.70  
  Purchase #4 $60.26   5.849%   $63.7846   $63.78   $63.80   $63.80  
  Purchase #5 $49.52   12.361%   $55.6412   $55.64   $55.65   $55.60  
  Purchase #6 $39.27   6.378%   $41.7746   $41.77   $41.75   $41.80  
  Purchase #7 $36.91   4.788%   $38.6773   $38.68   $38.70   $38.70  
  7 purchase totals = $426.48       $468.5586   $468.55   $468.60   $468.60