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 $112.33   10.168%   $123.7517   $123.75   $123.75   $123.80  
  Purchase #2 $165.82   13.776%   $188.6634   $188.66   $188.65   $188.70  
  Purchase #3 $158.28   8.460%   $171.6705   $171.67   $171.65   $171.70  
  Purchase #4 $221.39   7.256%   $237.4541   $237.45   $237.45   $237.50  
  Purchase #5 $53.34   12.585%   $60.0528   $60.05   $60.05   $60.10  
  Purchase #6 $203.50   7.610%   $218.9864   $218.99   $219.00   $219.00  
  Purchase #7 $82.58   11.426%   $92.0156   $92.02   $92.00   $92.00  
  7 purchase totals = $997.24       $1,092.5945   $1,092.59   $1,092.55   $1,092.80