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 $219.83   9.629%   $240.9974   $241.00   $241.00   $241.00  
  Purchase #2 $153.92   11.444%   $171.5346   $171.53   $171.55   $171.50  
  Purchase #3 $156.83   12.609%   $176.6047   $176.60   $176.60   $176.60  
  Purchase #4 $53.94   5.343%   $56.822   $56.82   $56.80   $56.80  
  Purchase #5 $189.84   12.105%   $212.8201   $212.82   $212.80   $212.80  
  Purchase #6 $197.81   7.436%   $212.5192   $212.52   $212.50   $212.50  
  Purchase #7 $20.60   11.674%   $23.0048   $23.00   $23.00   $23.00  
  7 purchase totals = $992.77       $1,094.3028   $1,094.29   $1,094.25   $1,094.20