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 $184.56   12.174%   $207.0283   $207.03   $207.05   $207.00  
  Purchase #2 $58.82   6.831%   $62.838   $62.84   $62.85   $62.80  
  Purchase #3 $87.68   13.305%   $99.3458   $99.35   $99.35   $99.30  
  Purchase #4 $208.38   6.695%   $222.331   $222.33   $222.35   $222.30  
  Purchase #5 $185.80   6.810%   $198.453   $198.45   $198.45   $198.50  
  Purchase #6 $25.57   6.333%   $27.1893   $27.19   $27.20   $27.20  
  Purchase #7 $120.57   6.775%   $128.7386   $128.74   $128.75   $128.70  
  7 purchase totals = $871.38       $945.9240   $945.93   $946.00   $945.80