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 $45.66   3.534%   $47.2736   $47.27   $47.25   $47.30  
  Purchase #2 $183.94   10.272%   $202.8343   $202.83   $202.85   $202.80  
  Purchase #3 $176.31   13.842%   $200.7148   $200.71   $200.70   $200.70  
  Purchase #4 $106.65   10.699%   $118.0605   $118.06   $118.05   $118.10  
  Purchase #5 $93.56   11.195%   $104.034   $104.03   $104.05   $104.00  
  Purchase #6 $124.47   11.497%   $138.7803   $138.78   $138.80   $138.80  
  Purchase #7 $66.69   10.808%   $73.8979   $73.90   $73.90   $73.90  
  7 purchase totals = $797.28       $885.5954   $885.58   $885.60   $885.60