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 $203.94   10.842%   $226.0512   $226.05   $226.05   $226.10  
  Purchase #2 $57.26   10.818%   $63.4544   $63.45   $63.45   $63.50  
  Purchase #3 $247.32   12.141%   $277.3471   $277.35   $277.35   $277.30  
  Purchase #4 $165.56   3.519%   $171.3861   $171.39   $171.40   $171.40  
  Purchase #5 $102.68   4.850%   $107.66   $107.66   $107.65   $107.70  
  Purchase #6 $77.49   13.303%   $87.7985   $87.80   $87.80   $87.80  
  Purchase #7 $112.50   4.606%   $117.6818   $117.68   $117.70   $117.70  
  7 purchase totals = $966.75       $1,051.3791   $1,051.38   $1,051.40   $1,051.50