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 $191.85   8.180%   $207.5433   $207.54   $207.55   $207.50  
  Purchase #2 $170.94   13.471%   $193.9673   $193.97   $193.95   $194.00  
  Purchase #3 $196.80   9.185%   $214.8761   $214.88   $214.90   $214.90  
  Purchase #4 $42.42   11.415%   $47.2622   $47.26   $47.25   $47.30  
  Purchase #5 $28.75   13.104%   $32.5174   $32.52   $32.50   $32.50  
  Purchase #6 $207.89   11.362%   $231.5105   $231.51   $231.50   $231.50  
  Purchase #7 $204.62   11.721%   $228.6035   $228.60   $228.60   $228.60  
  7 purchase totals = $1,043.27       $1,156.2803   $1,156.28   $1,156.25   $1,156.30