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 $130.87   8.518%   $142.0175   $142.02   $142.00   $142.00  
  Purchase #2 $95.71   12.162%   $107.3503   $107.35   $107.35   $107.40  
  Purchase #3 $191.32   7.847%   $206.3329   $206.33   $206.35   $206.30  
  Purchase #4 $57.96   8.156%   $62.6872   $62.69   $62.70   $62.70  
  Purchase #5 $200.69   12.234%   $225.2424   $225.24   $225.25   $225.20  
  Purchase #6 $216.68   8.718%   $235.5702   $235.57   $235.55   $235.60  
  Purchase #7 $29.84   13.434%   $33.8487   $33.85   $33.85   $33.80  
  7 purchase totals = $923.07       $1,013.0492   $1,013.05   $1,013.05   $1,013.00