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 $241.47   11.390%   $268.9734   $268.97   $268.95   $269.00  
  Purchase #2 $183.85   10.372%   $202.9189   $202.92   $202.90   $202.90  
  Purchase #3 $166.92   11.507%   $186.1275   $186.13   $186.15   $186.10  
  Purchase #4 $240.60   8.226%   $260.3918   $260.39   $260.40   $260.40  
  Purchase #5 $43.51   3.760%   $45.146   $45.15   $45.15   $45.10  
  Purchase #6 $110.93   10.156%   $122.1961   $122.20   $122.20   $122.20  
  Purchase #7 $100.86   11.403%   $112.3611   $112.36   $112.35   $112.40  
  7 purchase totals = $1,088.14       $1,198.1148   $1,198.12   $1,198.10   $1,198.10