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 $54.44   8.551%   $59.0952   $59.10   $59.10   $59.10  
  Purchase #2 $85.39   9.694%   $93.6677   $93.67   $93.65   $93.70  
  Purchase #3 $206.90   11.259%   $230.1949   $230.19   $230.20   $230.20  
  Purchase #4 $227.62   9.712%   $249.7265   $249.73   $249.75   $249.70  
  Purchase #5 $227.82   11.734%   $254.5524   $254.55   $254.55   $254.60  
  Purchase #6 $155.98   6.702%   $166.4338   $166.43   $166.45   $166.40  
  Purchase #7 $24.73   9.215%   $27.0089   $27.01   $27.00   $27.00  
  7 purchase totals = $982.88       $1,080.6794   $1,080.68   $1,080.70   $1,080.70