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 $54.92   11.639%   $61.3121   $61.31   $61.30   $61.30  
  Purchase #2 $113.49   6.289%   $120.6274   $120.63   $120.65   $120.60  
  Purchase #3 $174.28   13.855%   $198.4265   $198.43   $198.45   $198.40  
  Purchase #4 $109.79   9.156%   $119.8424   $119.84   $119.85   $119.80  
  Purchase #5 $223.43   9.653%   $244.9977   $245.00   $245.00   $245.00  
  Purchase #6 $12.36   10.641%   $13.6752   $13.68   $13.70   $13.70  
  Purchase #7 $162.84   5.158%   $171.2393   $171.24   $171.25   $171.20  
  7 purchase totals = $851.11       $930.1206   $930.13   $930.20   $930.00