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 $184.64   12.391%   $207.5187   $207.52   $207.50   $207.50  
  Purchase #2 $243.57   6.751%   $260.0134   $260.01   $260.00   $260.00  
  Purchase #3 $75.82   6.637%   $80.8522   $80.85   $80.85   $80.90  
  Purchase #4 $186.48   11.506%   $207.9364   $207.94   $207.95   $207.90  
  Purchase #5 $192.48   4.769%   $201.6594   $201.66   $201.65   $201.70  
  Purchase #6 $106.61   11.346%   $118.706   $118.71   $118.70   $118.70  
  Purchase #7 $185.25   8.863%   $201.6687   $201.67   $201.65   $201.70  
  7 purchase totals = $1,174.85       $1,278.3548   $1,278.36   $1,278.30   $1,278.40