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 $206.64   12.287%   $232.0299   $232.03   $232.05   $232.00  
  Purchase #2 $147.54   3.475%   $152.667   $152.67   $152.65   $152.70  
  Purchase #3 $104.56   7.747%   $112.6603   $112.66   $112.65   $112.70  
  Purchase #4 $22.61   10.731%   $25.0363   $25.04   $25.05   $25.00  
  Purchase #5 $228.30   3.265%   $235.754   $235.75   $235.75   $235.80  
  Purchase #6 $44.28   12.783%   $49.9403   $49.94   $49.95   $49.90  
  Purchase #7 $174.77   12.842%   $197.214   $197.21   $197.20   $197.20  
  7 purchase totals = $928.70       $1,005.3018   $1,005.30   $1,005.30   $1,005.30