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 $189.89   12.428%   $213.4895   $213.49   $213.50   $213.50  
  Purchase #2 $52.92   7.184%   $56.7218   $56.72   $56.70   $56.70  
  Purchase #3 $29.67   13.826%   $33.7722   $33.77   $33.75   $33.80  
  Purchase #4 $233.61   3.272%   $241.2537   $241.25   $241.25   $241.30  
  Purchase #5 $210.30   4.443%   $219.6436   $219.64   $219.65   $219.60  
  Purchase #6 $193.33   4.494%   $202.0183   $202.02   $202.00   $202.00  
  Purchase #7 $54.45   7.280%   $58.414   $58.41   $58.40   $58.40  
  7 purchase totals = $964.17       $1,025.3131   $1,025.30   $1,025.25   $1,025.30