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 $68.44   10.830%   $75.8521   $75.85   $75.85   $75.90  
  Purchase #2 $121.70   6.148%   $129.1821   $129.18   $129.20   $129.20  
  Purchase #3 $155.80   7.532%   $167.5349   $167.53   $167.55   $167.50  
  Purchase #4 $205.74   10.150%   $226.6226   $226.62   $226.60   $226.60  
  Purchase #5 $92.56   10.195%   $101.9965   $102.00   $102.00   $102.00  
  Purchase #6 $127.51   12.503%   $143.4526   $143.45   $143.45   $143.50  
  Purchase #7 $214.89   4.731%   $225.0564   $225.06   $225.05   $225.10  
  7 purchase totals = $986.64       $1,069.6972   $1,069.69   $1,069.70   $1,069.80