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 $92.27   12.102%   $103.4365   $103.44   $103.45   $103.40  
  Purchase #2 $216.95   9.547%   $237.6622   $237.66   $237.65   $237.70  
  Purchase #3 $223.71   10.336%   $246.8327   $246.83   $246.85   $246.80  
  Purchase #4 $73.53   9.620%   $80.6036   $80.60   $80.60   $80.60  
  Purchase #5 $204.85   3.187%   $211.3786   $211.38   $211.40   $211.40  
  Purchase #6 $110.78   4.562%   $115.8338   $115.83   $115.85   $115.80  
  Purchase #7 $76.93   6.167%   $81.6743   $81.67   $81.65   $81.70  
  7 purchase totals = $999.02       $1,077.4217   $1,077.41   $1,077.45   $1,077.40