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 $57.52   7.177%   $61.6482   $61.65   $61.65   $61.60  
  Purchase #2 $202.94   8.324%   $219.8327   $219.83   $219.85   $219.80  
  Purchase #3 $134.81   9.815%   $148.0416   $148.04   $148.05   $148.00  
  Purchase #4 $171.26   11.114%   $190.2938   $190.29   $190.30   $190.30  
  Purchase #5 $121.55   11.233%   $135.2037   $135.20   $135.20   $135.20  
  Purchase #6 $51.50   9.142%   $56.2081   $56.21   $56.20   $56.20  
  Purchase #7 $184.60   11.764%   $206.3163   $206.32   $206.30   $206.30  
  7 purchase totals = $924.18       $1,017.5444   $1,017.54   $1,017.55   $1,017.40