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 $74.51   4.160%   $77.6096   $77.61   $77.60   $77.60  
  Purchase #2 $200.82   9.283%   $219.4621   $219.46   $219.45   $219.50  
  Purchase #3 $50.93   3.661%   $52.7945   $52.79   $52.80   $52.80  
  Purchase #4 $23.76   3.353%   $24.5567   $24.56   $24.55   $24.60  
  Purchase #5 $87.74   4.324%   $91.5339   $91.53   $91.55   $91.50  
  Purchase #6 $167.94   3.408%   $173.6634   $173.66   $173.65   $173.70  
  Purchase #7 $134.54   13.158%   $152.2428   $152.24   $152.25   $152.20  
  7 purchase totals = $740.24       $791.8630   $791.85   $791.85   $791.90